It varies from one fanfiction to another. Some fanfictions might depict Naruto as dead to introduce a new set of challenges for the remaining characters. For example, if Naruto dies, Konoha might be left vulnerable, and characters like Sasuke or Sakura would have to step up in different ways. But there are also plenty of fanfictions where Naruto remains alive and continues his journey, perhaps facing new and even more dangerous threats than in the original series.
Well, it's a bit complicated. Sometimes Superman survives all the challenges and remains alive, while in certain story arcs, he might encounter events that lead to his apparent death. But often, there's a way for him to come back or for the situation to have a twist.