Sakura could be involved too. She might be worried about Naruto's condition and try to find him after he escapes. Or she could be the one assigned by Tsunade to bring Naruto back to the hospital.
Tsunade for sure. As the Hokage and also a medical expert, she would be furious about Naruto escaping the hospital. She might send some ninjas to bring him back.
Sasuke could be involved. He and Naruto often have intertwined stories. Sasuke might either be an ally in Naruto's destruction of Iwa, or he could be there for his own reasons, like seeking power or revenge.
Sasuke could be involved. Since they have a complex relationship, Sasuke might either be a rival during Naruto's training, pushing him to be better, or he could end up joining Naruto in some training sessions to become stronger together.
Sasuke is an obvious choice. He has a connection to Naruto that goes beyond just friendship or rivalry. He might be the one who first discovers Naruto's predicament and sets out to find a solution. Sakura is essential too. Her skills as a medical ninja are crucial. She could be the one who patches Naruto up every time he gets injured in his fight against whatever is threatening his life. Also, characters like Jiraiya might make an appearance. Even though he's dead in the original story, in this fanfiction, he could come back as a spirit guide to help Naruto find a way to 'refuse to die', giving him advice based on his own knowledge and experiences.
Sasuke is likely to be involved. He and Naruto have a complex relationship and Sasuke has become an ally. He could offer his strength in combat to protect the rebuilding efforts. Also, Sakura. She's a skilled ninja with medical abilities that could be useful if there are any injuries during the process.
Hinata would also be very involved. She has deep feelings for Naruto. She might be at his bedside in the hospital, praying for his recovery. After his death, she would be heartbroken and might have to find a new purpose in life without Naruto.
Sasuke would likely be involved. He has his own issues with Konoha and might side with Naruto, either out of friendship or his own vendetta against the village. Also, the elders of Konoha like Danzo could be important characters as they might be the ones behind Naruto's banishment.
Sasuke could be involved. Since he has a complex relationship with Naruto, if Naruto becomes 'Red X', Sasuke might be either an ally or an antagonist depending on the nature of 'Red X'. Another character could be Kakashi. As Naruto's mentor, he would surely notice the change and try to guide Naruto through it.
Sasuke is very likely to be involved. Since he's Naruto's rival and friend, he might be there to witness the meeting of different Narutos. He could be confused at first, but then he'd probably try to figure out how this strange phenomenon occurred. He might also get involved in battles or discussions that the Narutos are having.
Sasuke is very likely to be involved. He has a close relationship with Naruto and is also an important figure in Boruto's life. His skills and knowledge could be crucial in any adventure or situation that Naruto and Boruto find themselves in. Another character could be Hinata. As Naruto's wife, she would surely be concerned about any strange events involving Naruto. And for Boruto, she is his mother, so she would play a role in any family - related or village - threatening situations.
Sasuke would most likely be involved. Since he has a strong bond with Naruto, he would sense something is wrong and try to free Naruto from Kaguya's control. Sakura might also be part of it as she cares about Naruto and would be determined to save him. Kakashi could play a role too, using his wisdom and experience to figure out a way to break Kaguya's hold on Naruto.