He could feel a sense of guilt. Sasuke might think that his actions or their relationship issues pushed Naruto to leave. He may then set out to find Naruto, not only to bring him back but also to resolve their long - standing issues. For example, if there were unspoken words or unresolved fights between them, Sasuke would see this as an opportunity to set things right.
They could face challenges from the ninja world's authorities who might see them as deserters. Other villages might try to capture them to gain an advantage over Konoha.
They might stumble upon a hidden village with a unique culture and way of life. This could lead to them learning new values and bringing those ideas back to their own village in the future. They could also meet new characters who become their allies or mentors along the way.
One possibility is that Naruto is on a quest for self - discovery. Leaving the village to find the Sage gives him a chance to be away from the familiar and face new challenges alone. He might encounter different types of enemies and allies during this journey. This could also be a way for him to prove himself not just to the village but also to himself. He wants to show that he can grow and become stronger without always relying on the village's resources.
Naruto might initially be in denial. He's so used to having Sakura around and believing that they have a future together. So when she leaves for Sasuke, he might think it's just a temporary thing or that she's been influenced by something or someone. But as time passes and he realizes it's real, he would be deeply hurt. He might also start to question his own self - worth, thinking that he wasn't good enough for Sakura. And he might even try to win her back at first, but then slowly come to accept the situation and focus on his other responsibilities like being a ninja and protecting the village.
It could be a village that focuses on both offensive and defensive capabilities. Naruto's ability to gather allies and Sasuke's strategic mind would make the village well - protected. There would probably be a council where they both have equal say. The architecture of the village might be a blend of Naruto's love for the traditional Leaf Village style and Sasuke's more modern and practical ideas. Maybe there would be a huge statue of both of them in the center, symbolizing their joint leadership.
Well, Naruto could leave the village in a fanfic due to a prophecy. He might believe that leaving is the only way to fulfill a greater destiny that the village can't support. As he leaves, he starts to explore different cultures of the ninja world. He learns about new forms of jutsu and how other villages operate. He could also form a team with outcasts from different villages, and together they strive to change the way the ninja world views things.
Obviously, Sakura herself is the main character. Naruto could also be in it. Maybe he tries to convince Sakura to stay or he could be the one to help her prepare for her journey. Sasuke might be another character. He could have some influence on Sakura's decision to leave, either by his own actions or just his presence in the village.
Perhaps Sakura leaves the village because she feels out of place. She might have had some falling - out with her friends or just doesn't feel like she belongs there anymore. So, she packs her bags and sets off on a solo adventure to find a place where she can truly be herself.
One possible plot could be that Sasuke leaves Sakura to pursue a solo mission of redemption. He feels that his past actions have left a stain on his honor and he must atone for them alone, believing that being with Sakura would only hold him back from his self - imposed penance.