This quest still buggy? *moan*
Here's what happened in a playthrough of mine:
I killed Servius and went over to him and picked "Leave him for dead but I forgot I was suppose to close a darkspawn hole in that mini dungeon with the giant as a "boss"
I closed the hole but it still registered a marker where Servius is supposed to be but he wasn't there.
The mission became permanently glitched.
So here's what I did in a different playthroughs:
I closed the darkspawn hole in the mini dungeon with the giant as a "boss" with two different characters.
I killed Servius and had one character pick "take him for questioning" while the other character I "leave him for dead"
The mission completed as normal.
I think the big factor that causes the mission to "glitch" is that dumb darkspawn hole you need to close in the mini dungeon. If you don't close the hole BEFORE YOU FIGHT SERVIUS then THE GAME WILL HAVE THIS QUEST PERMANENTLY BE INCOMPLETE.
Dumb but it seems to be true. Maybe they should seal the exit door leading to servius or something to have this mission be unglitchable.