Well, one possible outcome could be that Naruto and Sasuke manage to defeat Madara through their combined strength and newfound powers. They might use their signature jutsus in a coordinated way that Madara can't counter.
In such a fanfiction, Naruto and Sasuke might win. They are both extremely powerful and their combined strength, like Naruto's Rasengan and Sasuke's Chidori, could overpower Madara.
A really interesting fanfiction could be set in an alternate universe where Sasuke never left the village in Naruto Shippuden. He and Sakura start to develop feelings for each other much earlier. They go through all the challenges of being young ninjas together, and their relationship blossoms as they face various threats to the village side by side, and they eventually get married and have a family.
Sasuke could also be the one. With his Sharingan and Rinnegan, he has unique abilities. He might use his Amaterasu in a very unexpected way, like creating a large - scale trap for Madara using the black flames. His intelligence and cold - blooded nature in battle make him capable of making a decisive move.
Sasuke is often a popular character in these fanfictions. He might play a role in helping Naruto against Madara or have his own motives during their battle. Kakashi can also be a prominent figure, perhaps using his Sharingan in a crucial moment to assist Naruto. Another popular character could be Hashirama, as his connection to Madara is a key part of the original story and can be further explored in fanfiction.
Another theme is redemption. Sometimes in these fanfics, Madara has a chance at redemption through his fight with Naruto. Naruto's belief in people's goodness can influence the outcome in such scenarios.
Sasuke's story wraps up in the final arcs of Naruto Shippuden. It's a complex and emotional ending that ties up his character development and relationships.
One popular storyline is about Naruto and Sasuke teaming up against a new, powerful enemy that threatens the entire ninja world. In this type of fanfiction, they put aside their differences and combine their unique skills, like Naruto's Rasengan and Sasuke's Chidori, to defeat the foe.
Naruto would probably win. He has an indomitable will and has always found ways to overcome powerful foes. His experience and the unique powers he might gain with the Rinnegan could give him an edge over Madara.