Actually in the Imperium section I covered how Atlantis used to be an Imperium territory mostly run by Poseidon's children but it separated and is in conflict with the Imperium. The city and it's territory is very much alive. However the core concept of the character is still workable. Your character could be a Dragon-blooded who wants to ursurp Atlantis for the Draconians or they could be Atlantean Royalty. If they're dragon blood perhaps his bloodline rides sea serpents instead of regular dragons.