Same general set up, same issue.
Knocked out Minthara before initiating dialogue. Long rest, Minthara disappeared. Killed the two other leaders and the rest of the goblin camp until nobody left. Freed Halsin, but stuck in "defeat the goblin leaders."
In my game, the quest log for "defeat the goblin leaders" indicates that Minthara and Gut have been defeated, while Dror Ragzlin still alive.
A separate quest, "save the refugees" says that Dror Ragzlin has been defeated and to talk to Zevlor. Talking to people doesn't help, throwing Dror's body into chasm doesn't help.
