Live as the Seneschal.
This is basically the end-game portion. You can only roam the streets of Cassardis and Gran Soren as a transparent, invisible figure. Your items will stay with you but you won't be able to use them. You won't be able to talk to the people but you can attack and kill them without repercussions.
To end the game and start New Game+, you have to return to the Seneschal chamber and use the Godsbane in your inventory.