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.
It could be a rogue ninja from another village who has a vendetta against Naruto. This ninja might have set a very elaborate trap that made it seem like Naruto was killed and left his body in a place where his friends would find him and think he was dead.
Maybe it's his father, Minato. Minato has a lot of things to tell Naruto, like more about the Uzumaki clan and how to better use the power of the Nine - Tails. And as his father, their connection is very strong, so it's quite possible that he is among the first dead Naruto talks to.
I'm not sure if there is an official one, but given the vastness of fanfiction on the internet, it's very likely that someone has written a Naruto - Isaac Dead Space fanfiction. Fanfiction writers love to cross over different fandoms to create unique and often strange stories. They might put Naruto characters in the Dead Space setting, or have Isaac somehow end up in the Naruto world.
Some fans might be drawn to dead Naruto fanfiction because it offers a different perspective. It can make them appreciate Naruto's character more by seeing how his death impacts the story. It also allows for exploring darker themes and different character developments that wouldn't occur in the main canon where Naruto survives.
Well, it could change the plot in many ways. For example, he might get some crucial information from the dead. Maybe he could learn some long - lost jutsu from a dead ninja master, which would make him stronger and help him in battles. Also, he could get some secrets about the Akatsuki's plans from their deceased members, which would give Konoha an advantage.
Well, first of all, the writers often take the unique elements from each universe. From Naruto, it's the ninjutsu, kekkei genkai, and the concept of the ninja villages. From Highschool of the Dead, it's the zombie apocalypse and the school environment. They then find ways to make these elements work together. Maybe a character with a Sharingan from Naruto can use its powers to detect zombies from afar. Also, they might use the character relationships. A Naruto character could form a team with some Highschool of the Dead survivors to face the challenges together. And they might also play with the different values of the two universes. For example, the loyalty in Naruto and the survival instinct in Highschool of the Dead.