Sim won't leave

I had an NPC at one my sim's house just the other day. I had exited the game, and restarted that game a few days later. The NPC was at my sim's house playing with my sim's telescope all night long in the game. I had to direct my sim to observed the sky in order to get that NPC stop playing with the telescope, and she did. And then she went home shortly after that. I don't know if this will work in your case, but it did in mine. But it's worth trying out to see if it will get that annoying NPC to go home in your game. :)