I don't recall having to do anything special to get out of the room...
The key Caracalla's ghost gives you is to get into Crowell's house in the first place. The teleporter to the dead-end room with the treasure is optional; the key to Caracalla's chest there can be found elsewhere in Aleroth:
on Caracalla's (burning) corpse at the south end of the Great Market plaza.
EDIT: loading a save and re-doing that part (I was wrong, you do need to keep all 4 corner candles lit), I had no problem simply leaving when the quest was done.
EDIT2: The barrier across the entrance of the room containing the ghosts should disappear as soon as the quest is complete. Other than that, just check your map; it should be open all the way back to the front door.
