In my Test they also dissapear when you have not escaped yet.
Definitely they do. I always assumed it was after fighting Kniles that they disappeared. Or perhaps if you fight Kniles before the Houndmaster.
It could be a timer I suppose but all I figured out (before leaving Fort Joy) for sure is sometimes they are there and sometimes they are gone.
Not a terribly helpful reply I know - it would be nice to know as they give decent XP.
