I've wondered about whether they will retake settlements as well.
The closest I've come to this is "vanishing" a fort and then the next day while I was fleeing a group of settlers I ran past the fort and there were men on the walls shooting at me. I came back to the fort the next day and there was one guy running out of the fort (patrol?) but the place was otherwise abandoned.
I have seen a covered wagon riding around. There is only one guy on it and the road is heavily patrolled. Maybe this will be some future method of restarting a settlement.
I would like the option to burn down a fort or to occupy it myself. At the least it would make them start from scratch. I feel like many of the settlements are stages of development. camp, logging camp, bivouac, fort. Each with more defenses like fences, buildings, walls. If they are going to retake them then it would be nice to make them start with the simple camp first.