If there are remaining hulks when the smasher goes down that are not killed, they will not despawn until the next Bazu Smasher spawns, which is about 2 hours.
One of these popped at the Ridgerunner/Aggressive camp not long ago, in the cove along the path to the raid mobs. They aggroed me instantly and chased me through the zone, camping my every move. Attempts to FD split them failed, I sat FD for nearly 30 minutes when they despawned.
Guessing it was around 30 minutes until they popped.. Hope that helps.