In general, the status of Naruto novels as canon can be a bit ambiguous. Some are closely tied to the main plot and characters, while others might be more like side stories or expansions that don't have a major impact on the core storyline.
In a fanfiction, we could explore a story where Kushina survives the Nine - Tails attack. She then gets to be a part of Naruto's growth, teaching him about his Uzumaki heritage and how to control the Nine - Tails in a more personal way compared to what Jiraiya taught him.
The canon story of Naruto pt 1 ends when Naruto and his friends graduate from the Ninja Academy and face various challenges, culminating in the battle against Orochimaru at the Chunin Exams.
It has a significant impact on the Naruto canon. In the original Naruto canon, there are no such storylines. If there is fanfiction about Naruto getting someone pregnant, it completely changes the character's path and the overall story direction. It's like adding a whole new and unexpected chapter that doesn't fit with the established lore. For example, Naruto's main focus in the canon was on becoming Hokage and bringing peace to the village. This new plot would divert his attention and character development in a very different way.
Well, it's popular because fans love seeing their relationship explored further. Naruto and Hinata's relationship in the original series was a bit under - developed in some ways. Fanfiction allows fans to flesh out their love story, see more of their interactions, and imagine their future together.
In the official Naruto canon, there is no such event where Naruto is banished because of Sakura fanfiction. The Naruto storyline follows a set plot created by the original author, and this kind of out - of - the - blue scenario doesn't exist in the real Naruto world.