I can't answer the first question as I've only had one villager leave and she asked if she could. I'm really curious about the "stealing villagers" thing too. I've had plenty of people visit and only be on my island for like 2 minutes and none of my villagers be anywhere near my visitor or me for my villager the next day to be like "so Blanky from Blankyland visited. Blankyland is really far away. I want to go to Blankyland someday." If the villagers already hint at maybe leaving one day I don't know if talking really affects anything unless the villager is already in boxes. I could be wrong though. We need someone else who has actual proof that a visitor talking to a villager can cause that villager to leave. However, with that said I agree with cheezu. I don't see how someone could "steal" a villager. I could see a visitor talking to a villager maybe increasing that villagers chances of asking to move out, but not getting the villager to leave without asking first.