Most blocks that have been blown up or burned down in a town that is under siege will be automatically regenerated by server.
Rollbacks take place at the end of a siege.
Blocks that are scheduled to be regenerated do not drop anything when destroyed. Storage blocks (e.g. chests) will be restored alongside their contents.
Only the blocks listed below are excluded from Automatic Rollbacks, and will not be restored at the end of a siege.