Alright, so I went after the goblin leaders one by one. I killed Gut by herself, then sent Minthara out on the raid with the intent to betray her and set a trap with the explosives I'd been hoarding all game.
Before I went to the raid, I took care of Ragzlin and the interior of the camp. When I went to the grove to talk to Zevlor to tip him off, he instead congratulated me on killing all three leaders.
It's like Minthara ceased to exist the second she left the fort. No fight, no goblins at the gate, no barrels buried in the dirt. Nothing. Wyll also congratulated me when I visited him in camp to regain my spell slots for the upcoming fight.
Anyone else have an issue with Minthara just... not existing anymore, after sending her on the raid?
