I play a game with only the conquest victory condition active;

When I decided to do the quest of mastery wildland anyway, I found that the big bad guy wasn't killed, thus not ending the quest. I noticed he was immobilized instead suggesting he was transported to a city.

I had discovered the Deorcnysse wildland and I checked; sure enough, he ended up there. Same thing with the Eblin demon quest; he also was not killed, but instead escaped, thus blocking that quest as well.

Only when I managed to capture the city did those quests end.