Are they gonna make the ex priest into a villain? Cuz all he's done so far is be inconsiderate, incompetent, and incarcerated.
He can be the egoistic villain who monologue their big villain plan out loud so the heroes can start preparing for it after dealing with him.
After all, someone has to inform the audience/characters about it and so far the dark elves/mr. evil mustache here are too competent to reveal much of anything.
My personal expectation:
The dark elves will treat him nicely for now, making him think they want the priests who's no longer faithful with them to have access to healing magic.
While in truth they'll probably observe his healing and try to figure out the process of human accessing healing magic...as well as how to BREAK it.
Maybe add in some bio weapon on top so once they can break healing magic of human then nothing can stop their threat to drop plague bomb that obviously they have the cure/vaccine to.