I had the same bug just happen to me.
Killed Gut.
Knocked out Minthara (stole the scroll that is in front of her to initiate combat).
Found and released Halsin.
Killed the third boss and all the other goblins -- no one is left inside the building.
Neither talking to Halsin nor Zevlor will advance either quest. Have long rested (multiple times), defeated the Hag and went to the Underdark and I'm still stuck.
