Unless Funcom changed the important server settings without an announcement, official servers are set to have followers decay in 14 (or was it 15?) days. Buildings decay in 8 days max (7 days of decay timer + 1 day of abandonment).
It’s really weird that the buildings would be left standing while the followers decayed.
The only thing I can find related to this is a short-lived discussion in TestLive forum, so it might actually be a bug that should have been reported back then but didn’t.
It ain’t gonna happen. I’ve been playing this game since early access, and Funcom’s policy has always been that they don’t reimburse you for your in-game losses, regardless of who’s responsible.