She's going to do that. 

She's also going to spend the entire time INTERNALLY FREAKING OUT about it. 

Doooooooooes she come back to find him still in the same condition as when she left him? 

He's resting!  With a Ring of Sustenance running, even!  Probably regained at least 1 more hit point about it, if things are happening continuously over time.

Merrin has no idea that her patient's physiology is not that of a normal dath ilani human! Or, well, she has noticed that multiple medical observations are not what she expected, but she doesn't even have the start of a hypothesis about it, except for ???narrative tropes??? because it would be a worse story if he didn't survive???? which is still not a form of logic she wants to put any real weight on. 

She's going to do all the same things that she would if she did know, because her priorities here are pretty overdetermined. She's just also going to be REALLY REALLY STRESSED the entire time. 

Merrin hurriedly weaves a basket-y stretcher structure between the two tent poles. She very very carefully transfers her unconscious patient from the ground onto it. She lightly ties him on with paracord.

....He's going to get at least second-degree sunburn like that. Merrin removes some of the pole segments and uses them and more paracord and adhesive strips to rig up a little tent over his head and shoulders. 

He's still not oxygenating amazingly on ambient air, though it seems to be totally stable and not getting any worse. Still. If he has a serious head injury, she really doesn't want any other factors reducing how much oxygen his brain is getting. She rigs up the O2 tubing again. 

Aaaaaaand off she goes. 

They're more than 1500 meters away from her camp, as the crow flies.

Which in some sense isn't that far, but she can't take a direct route, not dragging a travois-stretcher. And Merrin is being pretty careful, and also she's stopping every five minutes to check on him, and every ten minutes to run down to the water and dunk herself because her suit cooling is badly overloaded and being out at this time of day with an open faceplate is riding the edge of heat exhaustion, and she's not able to push it that quickly because, again, if she gives herself heatstroke trying to move him faster then she won't make it back to camp at all. She can ignore being dizzy but she's going to stop for a cool-off break every time she starts getting nauseous.

Her patient's body temperature is continuing to be remarkably normal but Merrin DOES NOT TRUST THAT. Once the IV bag is empty, she snips off one end to turn it into a collapsible water-carrying container, and she'll carry up bagfuls of cold seawater and dump them on his torso to, hopefully, counteract the heat of the sun. 

It's going to take her like seven hours to walk that distance, under the conditions described. Also, while she can avoid inflicting any further lethal damage, she is going to be doing quite a lot of jarring his broken limbs and making bone shards grind against each other, and will probably in fact be inflicting nonlethal damage in the process of trying to move him. 

At least the sun is slowly getting less hot! By 48:00 local time, it's down to only 29° C and 75% relative humidity! No longer heatstroke territory for either of them! 

(Sunset isn't due until around 50:30 local time, so at least she has light to navigate by the whole way.) 

Merrin is checking on him a minimum of every ten minutes (and has the vital sign monitors on him programmed to do auditory alarms, though she can't sync them to the wrist display on her armor, that part of her suit's electronic capabilities broke a planetary-month ago and did not seem like a big enough deal to prioritize cannibalizing other electronics to fix.) 

Any significant changes over the journey, especially to his breathing, that might for example prompt her to stop and try additional emergency treatment where she is? 

2 hours of rest (with a Ring on) would be good for recovering 12 HP and another 12 of nonlethal, modulo any more nonlethal that got accidentally inflicted.  It won't wake him up if there's been no other Heal applied to him, but he might start to react to things even if he doesn't wake up.

Merrin is not going to miss that! It's a really reassuring sign! If his level of consciousness is improving at all, rather than getting worse, then he probably doesn't have active intracranial bleeding right now. Not that she can CHECK because she HAS NO DIAGNOSTIC EQUIPMENT, why didn't she put the portable ultrasound in her emergency bag, oh right because it weighs 0.9kg and takes up a substantial volume and she was instead using that weight and volume allotment for her tent poles and emergency blanket. At least she HAS it in working order. If his respiratory status gets worse tonight she's going to be SO inconvenienced tonight by the fact that she dismantled her portable ventilator to turn it into a cave-ventilator. 

(She's still mentally tracking that he probably got some radon exposure to his lungs and this could show up as pneumonitis in a day or two, even if she at no point actually detected radioactivity and that puts a cap on how severe the exposure could have been. There's absolutely nothing she can do about it one way or another; the damage is already done.) 

Merrin makes it back to her campsite at 48:12, a little over two hours before sunset. 

Her shelter is as she left it, still in "day" mode with the tarp stretched overtop of it for maximum sun reflection (with an air gap for additional heat insulation, so that any solar heat absorbed by the tarp itself will not be in direct contact with the roof.)  

The temperature inside is only 19° C and the humidity is 62%. She'll be downright comfortable! All of her gear is exactly where she left it. It's not like there's anyone else around to mess with it.

Merrin had a three-hour nap between 27:00 and 30:00 local time, but that was 17 hours ago, and before that she woke with the planetary dawn at like 13:00, so she's been awake with only the one nap for the last 35 hours. 

She's tired. And hungry, and thirsty, and frustrated, and she's been using a lot of her emotional regulation capacity on not being the bad kind of stressed-and-upset that makes her worse at things. 

She's also a trained Exception Handling medic and none of that matters. 

She hauls her unconscious boyfriend into her tent and - ugh - dismantles the sleeping pad and sleeping bag setup from her pod, to have something to put him on that isn't the gravel floor. 

She drinks a liter and a half of water with a bit of sea salt and bladdersac syrup in it. (Sea salt from this planet has a tiny bit of dissolved uranium in it, but not really enough to be a problem, unlike eating filter-feeders.) She considers that if she's feeling dehydrated then presumably Estha is worse off, and she digs out another of her remaining, like, 3L total of safe IV fluids. She probably does actually have what she needs here to make sterile saline but she hasn't prioritized it because she did NOT KNOW THIS WAS GOING TO HAPPEN. 

...She'll do a whole lot of labs, because she might as well when she has the equipment, and she'll examine him with the portable ultrasound. First priority is to confirm if he has a skull fracture and whether the bone is actually displaced or just cracked, and check for additional intracranial bleeding – if it's not a displaced skull fracture and there's no bleeding putting pressure where it shouldn't, her best bet here given her facilities is to just leave it alone. 

The skull fracture didn't take him below 0HP, so there's no ongoing intracranial bleeding.  The vitality that flows through a 6th-circle cleric is serious stuff.

Every one of her labs that relates to food or water, from blood glucose to potassium to sodium, is going to indicate that Esta is well-fed and well-hydrated...

Unless at some point Merrin makes the terrible awful no good very bad mistake of taking those innocent-looking metal rings off his fingers?  Maybe for fear of swelling?  Other potential horrendous mistakes would include taking off Esta's belt of +4 Constitution!  Just in case Merrin is feeling insufficiently enriched by her current state of medical emergency.

Once she's confirmed - to her relief and also some confusion - that there's no bleeding in his brain, then Merrin is going to scan his arms to actually map out the broken bones in order to splint them. If there are any hand fractures, then yeah, trying to get any rings off him before his hands swell enough to a) make it impossible to remove the rings without a saw that can cut metal (assuming they aren't already at this point that swollen) and b) cut off circulation to the finger as a result, is going to be a priority! 

(If Merrin were less utterly exhausted, she might spend more time considering whether additional swelling is that likely when it's already been like eight hours since the initial injury, or she might question her prior that he's dehydrated and will get a lot more swelling as soon as she gets IV fluids into him, given that his labs show no sign of dehydration. But Merrin is exhausted and operating heavily on automatic trained habits right now, and "absolutely do not leave rings on patients with arm or hand fractures, literally why would you do that" is a trained habit.) 

(She's ignoring the belt for now). 

Welp!  That's not going to produce any instant feedback that might tell her she did something wrong.  But it sure ain't gonna help anything later!

His arms are pretty fucked up, but he has good circulation to his fingers and Merrin thinks she can probably splint his arms so that all the bones are in roughly the right place to heal. She would really, really prefer to avoid having to surgically pin bones in place, it's going to be more or less impossible to set up an actual sterile operating theater in her cave. (Not to mention she's tired enough to know on priors that she's impaired.) 

She'll give him IV painkillers FIRST, because she has them and does not actually intend to torture him on purpose here, and he's breathing fine and also she can now switch him to the oxygen concentrator and it goes up to 4L/min if he gets respiratory depression. And then she'll spend most of the next 90 minutes trying to unfuck his arm bones a bit and then properly immobilize everything so it has a chance of healing correctly. 

Merrin is watching him closely for any signs of consciousness. 

He's already rested for 2 hours (= 8 hours, before SOMEBODY TOOK OFF HIS SUSTENANCE RING) and can't just do that part again.  But all that has got to count as Treat Deadly Injuries, which is good for another 17hp -- Merrin has got to be making these rolls by more than 5 -- plus 17hp of nonlethal damage cured too...

Which amounts to a total of 29hp of lethal damage cured, and 29hp of nonlethal damage...

And that's not gonna take his total lethal damage + nonlethal damage under 87, because Esta was frankly not doing totally great with all that underwater battering before he drowned and then got dragged over rocks with a bunch of broken bones.

Next up on Esta's potential healing schedule:  A full day's rest, or Long-Term Care if some Healer cares to put in 8 hours of light work about it.

Merrin is so tired but she's not going to feel confident that he's actually stable and recovering until she sees more signs of improvement to his mental status.

She takes more stimulants. 

...She finally thinks to remove the armor and plug it into her main battery, and she changes into her robe. She actually has three robes, at this point, and they're just her routine clothing when it's not so cold that she needs to be wearing all of her layers at once.

...She is eventually going to get around to cutting off the rest of his clothes so she can get a good ultrasound view of all his internal organs and check for bleeding.

(She'll have to really bundle him up later to keep him warm, or...cuddle him? or something? But it takes a nice long time for the cave to cool down even after sunset, it's still 17° C, she's not worried about his body temperature if he's in the sleeping bag.) 

This will, unfortunately, involve her trying to remove the belt. 

Removing Esta's +4 Belt of Mighty Constitution will drop his CON from 13 (+1) to 9 (-1), corresponding to a loss of 24 hit points off his previous maximum of 87.

Esta seems to be suddenly doing MUCH worse right after Merrin happens to finish removing the belt!  Like falling into a tidal bore twice, or like undoing most of her previous work on treating him!  This is no doubt a total coincidence.