I have the same bug issue. I fought Maelwald around 15 hours ago, when I was still getting used to PoE. My characters died, but my main had something like 10 endurance left. Instead of fighting me Maewald up and fled into the next room where the spiders promptly killed him. At the time I thought this was part of the game. So I went upstairs, told the spirit that he is dead, and started exploring and learning the lore. But the Maewald quest is still open in my quest box. I never got the option to release his soul, etc. I wandered around the different levels of the keep thinking Maewald survived and I have to get him. Found out about the bug after I got suspicious that I can't get to Elm's Reach with the ambassador, apparently a river is supposed to dry up through another quest after Maelwald is gone.
Since then I lost the pre-fight save file, and have invested many hours into the game so don't really want to start over. Is there anyway to finish the quest and move on in the main story line?