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.
Kasumi is often a popular choice. Her status as a main character in the 'Dead or Alive' series and her unique ninja - like fighting style make her interesting to incorporate into crossovers. She can bring an element of mystery and agility.
It could be about various things. Maybe it's a story centered around characters who are constantly in life - or - death situations. It might involve themes of survival, danger, and the choices one has to make when faced with the possibility of death.
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.