The quest to rescue the mage triggers when you arrive at the plaza at the bottom of the stairs. The Imperial Commander can be killed safely with totems from above the stairs. If that approach is chosen, the quest will not advance and the zone has to be reset.
Expected behavior:
I kill the imperial commander and his minions from the top of the stairs with totems. I walk down the stairs, trigger the quest and the quest state recognizes that the target was already killed. The quest advances normally.
Actual behavior:
The imperial commander is killed from above with totems. When walking downstairs to trigger the quest, nothing happens. The quest to free the mage starts, but never completes despite the commander already being dead.