The trick to rising in Asmodeus's hierarchy, according to the forces of Chaotic Good, is to get enough circles while you're still at the Worldwound. If you do it that way, the Iomedaeans and such will get mad if anyone kills you. Otherwise—well, being an Asmodean cleric very much makes you a priority target for any other adventuring parties you get into a spat with.

It's not that you're more likely to decide the battle than the other members of your party. It's that your wizard buddy isn't going to be the one casting malediction.

He's not an idiot. He prepared Greater Infernal Healing.

Ugh, that's not going to be good enough is it. Damn.

It's not unheard of for souls to go missing in their trip along the River of Souls. Almost all souls out of Creation end up there, and where there is free energy, there is something that wants to eat that free energy, namely daemons of Abaddon that hunger past the confines of their home plane. Angels and devils and well-paid axiomites are well aware of this, and do their part in defending the River, Worldwound in macrocosm.

Really, the only innovation here is the thing that's taking Carrera's soul! 

A let's-call-it-a-hand plucks Carrera out of the River of Souls, and carries it somewhere Else. And while, along the River, Carrera would be asleep or amnesiac, with no body to form memories with, this hand sees fit to, on its path, construct form for Carrera, and so he does catch some glimpses of what he's being carried through, beyond mortal comprehension as it is.

...something sort of like a golem that knows everything and, because of this, necessarily because of this, greatly likes being slime...

...a slave at the bottom of a Tyranny, and also at the top...

...being watched from everywhere in a way that is also mathematical-methods...

...a VERY LOUD GREETING by something that wants something...

And many other things besides, all at the same time.

That these are written as full sentences might mislead one as to how much sense they're making. Carrera just died, and he's a mortal, and none of this is deliberate communication (surely?). You'd have as easy a time explaining all this to Asmodeus; the gap is about as large.

And then Carrera is dropped somewhere else, sensate once more!

He has his arms, and his legs, and his spells.

It is very hot, and very bright. 

...maybe that's what not remembering your trial before Pharasma feels like. Carrera is not quite sure why that would feel like this, but maybe it feels like this.

Why does Avernus have a blue sky. In Visions of Hell it's usually red or yellow.

...why does he still have spells.

Part of him breathes a sigh of relief. Which is, he supposes, probably the whole point of presenting him with something this confusing. Hell has to give him hope if it wants to be able to destroy it.

It's not going to work on him.

Can he climb the wall of valley he's in? Probably he is not meant to just stand around doing nothing.

The inhalation part of any sigh of relief would also include pulling some burning-hot air into his lungs. As would normal breathing. Take 2 points of fire damage, and another 1d6 each minute.

If he's still up for climbing - he might be, I'm sure as an obedient slave of Asmodeus he's not squeamish about a little fire damage - then sure, he could climb the wall, there are enough handholds and flat bits that it doesn't take expertise to do so. But it's quite a ways to the top, if he was alive I'd doubt his physical ability to make it in the heat.

He would find the rocks are painfully hot to the touch, too, but far from so much that he couldn't hold tightly if he wanted.

So what, he's at -15 HP now, and slightly deader than before? Or did he get healed, and he's 2 HP shy of perfect shape? Somewhere in between?

If his backup scrolls survived his death instead of only his arms, legs, and spells—he would like to cast Endure Elements. It is hot enough to be hazardous, rather than just unpleasant. And he'll try Creating some Water all over himself, if he can't make the problems all go away with Endure Elements.