If the hermit dies another one will be called. Its also possible if there is not enough sims spawn in the world, that some sims will not show up. I have noticed this in the spa day spa, the two rooms in my spa had 2 refliectionist and only one therapist, but the venue had 2 massage tables, one of the therapist died and there was no one in the game qualified to fill that position, so the game never filled it, however to fix it just click hire a message therapist and a new message therapist will be spawned, now there is someone to fulfill the job so the next time you come back the message therapist will show up when you load the lot.