So sorry this happened to you! But as a person who was a vengeful teen to awful people back in New Leaf, my advice to you is this: A person can destroy 50% of your island from the time it takes to cross it. I understand that you wanted to be kind and let them leave instead of ending or resetting the session, but you should've just reset the moment he came in because getting out of your house may take ages. I always do that in the case that I get some random in my town.