Merrin is not grimmer than usual! Merrin has had six planetary months to absorb her situation, and her situation is not, in fact, worse than it was before, if it turns out Estha getting [spells] from his [god] was a one-time thing. They'll die eventually, probably, but with each other for company, which from Merrin's perspective right now is almost certainly better than not that. And their chances are better even if Estha never gets another [spell], she thinks? He's got his [belt] so he can keep up with her; they can do construction projects and exploration projects that would be too difficult or dangerous solo! Feeding both of them on local biomass will be an enormous hassle but not, necessarily, intractable...
And maybe he will get [spells] again! It seems odd to Merrin that his [god] would be able to transmit those exactly once? Like, low confidence because she has no idea how anything works, but what would even be the mechanism of that?
She is going to do her very best to eat all of the food that Estha made for her, since she was warned it won't be good anymore after 24 hours (and, given that it's magic, she's dubious that attempting to frantically freeze-dry or pickle it before that interval elapses will even help.) A Merrin full of (relatively) delicious calories is a Merrin in a much better mood than her average over recent months.
She should probably, at some point, do her own pondering on the larger situation – it's such a weird situation! – but she has no idea how to get any further on making inferences unless she jumps headfirst into the Narrative Trope Logic and she is not quite resigned to that yet.
Productive logistics planning she can make progress on now: starting to map out plans for riverbed-searching, under various assumptions including "no more [spells] ever, just Detect Magic", in which case they need to time it for both low tide and times of day when being outside without shelter or climate-protection won't be immediately lethal.
(Also, unless Estha interrupts her to object, she'll get out her shelter repair kit - which includes sewing materials as well as a lot of other materials - and start fixing his clothes; it hasn't occurred to her that this would be a good use of a [spell] even if he gets more, since she wasn't actually aware they had any magical features, and in any case she can at least get him something repaired enough to be wearable-for-warm in less than eight hours.)