Good question. I think if some of them feel they can lure in new people, and the Horror (being almost godlike in its abilities) knows they'll come back, then they can leave. Co-GM agrees and thinks that maybe certain residents are sent out for up to years at a time, even starting families, with that inexorable tug to return once they need to find somewhere to 'settle down'.

I'd want to restrict visitor applications if possible and go for residents. Visitors don't have as much of a presence in the story and it'll make things clunky as we progress, because the Horror will almost definitely start making visitors move out once it smells trouble.