At first, Boruto would be in shock. But then, he would likely be filled with a new - found determination. He would vow to become as strong as Naruto, if not stronger. He'd study Naruto's techniques more intently and strive to protect the village in Naruto's place. Boruto would also carry the weight of Naruto's legacy on his shoulders, which would shape his actions and decisions in the fanfiction.
Boruto would be a mess of emotions. He'd feel guilt, grief, and a burning desire for revenge all at once. He might lash out at those around him in his pain. However, over time, he would start to channel those negative emotions into positive growth. He'd remember Naruto's teachings and use them to become a better ninja. His relationship with his friends and family would also change as he tries to come to terms with Naruto's death in this fanfiction scenario.
Boruto's reaction would be complex. He'd be heartbroken, for sure. He might start to question his own worth and purpose. But over time, he'd realize that he has to carry on Naruto's legacy. He'd become more serious and focused. He'd also become more empathetic towards others, understanding the weight of sacrifice. He might even start to study Naruto's techniques and leadership style more closely, trying to emulate the things that made Naruto such a great Hokage and hero.
She would be devastated. Hinata has deep feelings for Naruto. His death would likely cause her to go into a state of shock and disbelief at first. She might blame herself for not being strong enough to protect him.
Naruto might also try to remember Sakura in a positive way. He would cherish the memories they had together. He could start initiatives in the village in her name, like promoting medical ninja training more, since Sakura was a great medical ninja. He would slowly turn his grief into a force for good in the village.
One possible plot could be that Naruto sacrifices himself to protect Boruto from a powerful new enemy. Maybe an ancient evil has been awakened and Boruto is in its direct path. Naruto, being the hero he is, steps in and uses all his power to stop it. His death then becomes a catalyst for Boruto's growth, driving him to become stronger and more determined to protect the village in Naruto's memory.
Perhaps there's a prophecy involved. The fanfic could be set up where it's foretold that Boruto will bring about a great change, but only if he survives a certain threat. Naruto, aware of this, sacrifices himself to ensure Boruto lives on. This could then trigger a series of events where Boruto has to deal with the political fallout in the village, as some may blame him for Naruto's death, while others see him as the key to the future. It could also lead to a rift between Boruto and some of his friends who struggle to understand why Naruto had to die for him.
Naruto would be devastated. Sasuke is his closest friend and rival. He would likely go into a state of deep mourning at first. He might isolate himself for a while, just trying to come to terms with the loss.
They could be shocked. Some might not expect the wild ideas that fans come up with in fanfiction.
Naruto would likely be excited. He loves his son so much that seeing different stories about Boruto would be like seeing different potential futures for him. He might even get some inspiration from the fanfiction to give Boruto some advice in real life.
Naruto would be devastated. He's always been one to value his friends deeply. He might initially go into denial and then be filled with rage, vowing to find out who or what was responsible for her death and seek justice. He would also likely carry a great deal of guilt, thinking that he should have been able to prevent it.
Sasuke would be deeply affected. He and Naruto had a complex relationship. He might feel regret for not being there to help Naruto and also feel a new sense of purpose in avenging his friend. Sakura would be heartbroken. She had always cared for Naruto, and his death would make her question the purpose of the ninja life. Haku herself would be in a state of shock and disbelief. She would feel a heavy burden of guilt, knowing that Naruto sacrificed his life for her. She might become more withdrawn initially but then use Naruto's memory as a motivation to become stronger.