Me and my thrall were fighting the Watcher in the Unnamed City when it fell off it’s platform. The 1st time it teleported back up in a fairly quick amount of time. Then it happened again. This time it also teleported back up in a timely manner. However, the 3rd time it fell off it never teleported back up. So I climbed down and low and behold found it had respawned under its normal spawn point.
I play SP, Exiled Lands with no mods.