Stuck at end of act 4

Quest marker wants me to "Find Tavakai," who I just killed. When he died he and Sin's sprites bugged and wouldn't move and wouldn't advance cutscene. I respawned at checkpoint and now all NPCs are marked as being at the final arena, but none are visible. Tried logging all the way out. Tried going back to town. Tried running final dungeon again.

I'm stuck at the end of Act 4 =(