Situation: Inside a faerie regio there is a tower. The players defeat the fae guardians, but don't actually raid the tower. They also didn't claim all the vis from the fae's bodies, because they couldn't find it. They return a year later to try to infiltrate the tower. Have the faeries regenerated, because their "story" -- their reason for existing -- is to guard this tower?
I'm asking from a RAW point of view, not from a "whatever makes the best story" pov.