When he's gone, don't forget to pick up whatever items have been dropped by all the recent enemies. You now have to go back to the main area of the tomb, so jump down all the way to the bottom of the tower and use the lift, striking the crystal corresponding to the first floor.
Approach the Judicar and listen to the conversation in which he pledges his obedience to the Lord of Bones. You'll also have a conversation with Basileus here, the last of the Dead Lords - you'll be looking for him in the newly unlocked quest [Basileus].
[TIP: From now you can summon two Dead Lords with the Interdiction ability, which means that you can solve even more of the game's puzzles.]
[TIP: Theoretically, you could proceed to the next main quest by The Gilded Arena from the world map. Nevertheless, I strongly advise reading the Closing the quest section to learn how to use the second enslaved Dead Lord to get to two previously inaccessible chests in the Judicar's Tomb.]