Or you can stack up on explosives, Misty step on the highest tower (the one to the right from the main door (ogre's point of view) and give them a hell of a party. Granted I did this on exiting the building in style thinking no one will know about the carnage inside but it was glorious!
You could also just load a save from the inside of the sanctum, unlock the moon door and head to the basement since there's a waypoint probably put in plače exactly so one could avoid this problem
