Perhaps the plot could involve some sort of magic or curse that is causing Naruto to be in this state. The story might then focus on how the Naruto world's medical ninjas try to figure out what's wrong. They could run all sorts of tests and experiments. And there could be a race against time as Naruto's condition worsens.
Maybe there would be a lot of emotional scenes between Rhodey and Tony. They could have heart - to - heart conversations about their past, their regrets, and their hopes. And Rhodey could also start to prepare for life without Tony, which would be a very difficult process for him.
In such a fanfiction, perhaps there would be a spiritual journey for Naruto. As he's dying while sealing the Kyuubi, he could have visions of his past, his friends, and his dreams. He might see the faces of Iruka - sensei who first recognized him, or Hinata's loving looks. This could give him the strength to complete the sealing process. After his death, the village could start to remember and celebrate his life in different ways. Statues could be erected in his honor, and his story could be told to every new ninja trainee as a legend of self - sacrifice.
Perhaps Naruto discovers some hidden powers or abilities that Kunou has inherited from him, which leads to a whole new adventure. They might go on a journey to understand and control these powers together. Also, Naruto could face challenges from the village elders who are not so accepting of Kunou at first.
Another plot development could be that with Sarutobi as his adoptive father, Naruto has access to different mentors. Sarutobi could call in favors from other great ninjas to train Naruto. This would expose Naruto to a wider variety of fighting styles and strategies. Maybe he gets trained by Kakashi earlier, or even has the chance to learn from some of the retired or older ninjas who usually keep to themselves.
Well, Naruto might discover some new Orochimaru's plan during the rescue. Maybe Orochimaru was trying to use Hinata to get some information about the Byakugan. After saving Hinata, Naruto could go on a mission to stop Orochimaru from achieving this goal with the help of his friends like Sasuke and Sakura.
Well, it could be about a disease that is slowly taking Sakura's life. Maybe she has some rare illness that the characters in the fanfiction are desperately trying to cure.
One possibility is that Naruto's friends launch a rescue mission. They would use their unique skills, like Sasuke's Sharingan or Sakura's medical ninjutsu combined with her combat skills, to find and save Naruto.
In a fanfiction with Naruto dying from cancer, the story might focus on how the ninja world reacts. His allies from different villages might come together to try and find a cure. However, Naruto, knowing the slim chances, might start to prepare for his death. He could pass on his teachings and the will of fire to the next generation in a more urgent and poignant way. His death could also lead to a shift in the power dynamics among the villages, as he was a unifying figure.
Well, one possible plot development could be Naruto training even harder to prove himself. After the Chunin Exams, he might seek out new jutsu or ways to improve his skills. Maybe he starts to focus on his control over the Nine - Tails' chakra more intensively.
One possible plot development could be that Naruto's friends in Konoha realize he's missing and start a search mission. They might suspect Kumo immediately due to the history of tensions between the two villages. Meanwhile, in Kumo, Naruto could be held in a secret location. Some in Kumo might want to use him as a bargaining chip against Konoha, while others might see his potential and try to turn him into an asset for Kumo.