...a thing Esta has sort of not been thinking about is the part where he has one (1) Heal spell.
It cures, among other effects, insanity.
If Asmodeus had granted him the two Heals that Esta had asked, it would have been obvious to use Heal spells on both of them.
Then, the obvious path-influencing meaning of his Lord granting Esta only one Heal spell, is that Esta is only meant to Heal himself of whatever debuffs he has taken from his encounter, and not Heal Mariona.
Why? Because it will not help Mariona? Because her insanity could not be cured that way?
But Mariona -- no, Merrin -- might have received ability damage or debuffs from any number of sources, like poor nutrition. It seems unlikely that a Heal spell would not do her some good; it is more comprehensive in its own way than even Regenerate.
So it may also be that it will not be advantageous to Asmodeus, if Merrin is cured. Perhaps her continued insanity would be useful to Him.
...Esta will see how this matter plays out, of whether Asmodeus seems to be steering or blind, in this place. And then he will choose what to do with his one Heal spell, before this spell-cycle ends; knowing, as he does, that he might receive no other Heal tomorrow, if he proves unable to ask.