In my mental drift time, I think of what could have happened to all the characters in Avatar. I wonder if Sokka and Suki could have made it work, considering how committed they were to their different homes, and I am sad to think that they may not have. I think Aang and Katara took up a nomadic life with Appa and Momo, living off the land with nothing more than what they could carry and spreading their messages of peace, love, and hope (and occasionally kicking people's asses when necessary). I believe Toph became captain of the Earth King's personal guard for many years, keeping them pure and honorable with the memory of the Dai Li fresh in her mind.
I believe that Zuko's example inspired near-religious fervor among Fire Nation youth, who would ritually scar themselves over their left eye and wander the world during their teenage years as Fire Nation Knights Errant. The Zukoites would explore the nations, seeking to do good and maintain balance, and in the end they did more to redeem the reputation of the Fire Nation than even Zuko himself. They and the Kyoshi Warriors remained stalwart allies and agents of the Avatar for generations.
I believe that Azula died in prison shortly after the events of "Sozin's Comet," a raving, paranoid, and broken individual who couldn't adjust to the new world that she couldn't control, and that Firelord Zuko grieved greatly over her loss, despite all that she had done.
Uncle Iroh retired to his tea shop in Ba Sing Se and lived a long, prosperous, and peaceful life, playing pai sho every day and dispensing the finest tea and the finest advice in the city. The day of his funeral was declared a day of mourning by the Earth King himself, with the line of citizens who came to pay their respects running for miles. The day was also marked by an unexpected solar eclipse that none of the court astronomers could explain.
In the world I see, Firelord Zuko visits his father in prison on the first day of every month and asks one question: "Where is my mother?" And every month, he returns to the palace, only to go back again the next month.
Maybe.
-- Ed