If they leave on their own from a clearing with a haunt you DON'T score VP, which is probably the biggest problem with the faction and one I spent a lot of time thinking about how to make work, and probably will spend more time on once the root jam is over. I didn't think you should score VP is when they leave on their own just because that would kind of cordon off these clearings from other factions for fear of giving you tons of VP, even when it's not your turn. However, I could see a version where you score 1 VP if someone moves 3 or more warriors out of a clearing with a haunt in a single move, or make it so when moving out of a clearing with a haunt, they have to leave at least 1 warrior behind. That would just mean messing about with their scoring some more, which honestly is a pretty good idea.
In regards to the second question, the building is kind of immortal as long as a haunt is on it, because I thought that would be a fun way to mess with the politics on the board in a new way!
Thank you for the questions and compliments, they mean more than you know!