There is still a chance the imp fix procedure will allow the murder quest to be finished, though I'm not sure if anyone has tried it in the download version of the game.
Mardaneus doesn't move until you complete one of the council quests (which is after going to the castle, leaving, finding Zandalor and doing a couple other things).
If the fix doesn't work, you could always use
iZakaroN's SaveEditor (or from
Kiya's site, with description) to give yourself a skill point to put into Restoration, to match the reward you would have gotten for completing the quest. I'd have to load an old save at that point to check how much experience is given (which depends on character level).
