Suggested by Paul
The Fire nation never found the avatar and the world was conquered and all that great stuff. After a bajillion years or so the spirits began devouring each other and became the Aedra and Deadra. After this the elder scroll series happened.
Aang awakes in the lake in Leawin and runs north towards Skyrim.
Due to Aangs nature as spirit bridge he is able to absorb a dragon soul and can travel to Oblivion.