The problem is, he is now 'trained' to his current life and won't come out on his own. I lived long ago in a place with other young people, and there was a cat who literally lived in the furnace 'closet' (not a room) and came out only once a day to get food and nothing else. That cat was disturbed (by then anyhow) and had a horrible life... which is partly why I'm so concerned about yours. He won't just decide to come out for no good reason anytime soon, even if he knows how to.