Some people reported problems telling Mardaneus about George's murder after he joins the council.
The vampire in the cave returned to his coffin at the back of the locked room after you sacrificed yourself. You need Lockpick level 2 to open the door, or Telekinesis level 2 to pull the lever inside on the wall. Don't forget to try to find the knight Markham again, who gave you the quest to investigate the cave (he starts on the path between Ars Magicana and the cave, but can wander around a lot).
