Hmm I could go with a realistic somewhat possible outcome or a crazy one....the latter has been chosen.

Aang manages to reach Ozai due to the help of his friends who are currently fighting their own battles. Aang starts losing and knows he needs a moment to turn into the avatar state, but Ozai not giving it to him. Fortunately or unfortunately Azula has lost all the last bits of her sanity and tries to take over by attempting to kill her father. Aang is able to get into avatar state due to this and renews his battle with Ozai as Azula falls unconscious, although not before seeing Aang win in her lack of sanity mind.

In other locations at time Toph kills 100 soldiers with rock spikes shooting through their hearts. Later when Katara scolds her on her methods Toph tells her "This not a cartoon show for little kids you know".

With Sokka and a near dead Suki, when outnumbered his sword starts glowing with energy from the moon and with one wild swing unleashes a wave of energy that would be ripping off a Bleach protagonist. Suddenly sees the spirit of Yue who saves Suki by merging with her.
Sokka: Suki?
Suki/Yue: Think its Yuki now.
Sokka: Alright a season ends without me losing a girlfriend or thinking of other girlfriend dying.

Aftermath

Aang gets a new vision telling him his next quest is to revive the airbenders and if can't find any must do it the old fashion fun way. Needless to say Katara was in a pmsing mood when he told her, so she won't be helping him in that quest. At same time a water tribe ship name Kataang sunk that day.
Aang discovers Ty Lee has airbender blood in her. One thing lead to another and she becomes his first wife. Some time later he discovers a very different Azula. The loss of sanity and last moments of the battle of her seeing him fight has morph her personality into a very wanting aggressive Aang fangirl. Due to things outside of his control while he was knocked out and tied up somewhere, she became the unofficial second wife of his harem.

Zuko becomes the new Fire Lord alongside with his trusted advisor his uncle and the future fire lady Mai, try to help their nation adapt to the aftermath of the war alongside the other nations. Rumor has it Mai sunk a ship named Zutara around time it was publicly made that she was to be married to Zuko.

Katara has swored off men and journies around helping people. Rumor has it she has a thing with the new Earth ruler.

Sokka married his two girlfriend fusion girl and lives happily. It seems he doesn't wear the pants of the family though. Also has a hobby of influencing plays that are about the avatar's journey to make his character look cooler and funnier.

Toph after defeating Bumi is declared his successor. The Earth King decides that he rather not have his title be just a title anymore and gives his region to her as well making her the new earth Queen. Some say the Queen takes a liking to women.

Years later Aang's kids see their father getting toss around by the Earth Queen in what suppose to be a friendly spar.