Itadori did indeed die in the manga. His death had a significant impact on the story and the other characters. It was a turning point that led to many new developments in the plot.
Itadori is quite powerful in the manga. His strength lies not only in his physical abilities but also in his determination and the unique powers he acquires along the way. He's able to face off against formidable opponents and come out on top more often than not.
Well, Itadori's journey in the manga has been full of surprises. He's had to deal with curses, make difficult choices, and his relationships with other characters have evolved in complex ways. There have also been moments of great personal sacrifice and growth for him.
I think young Sasuke would have a very intense reaction. He was so consumed by his hatred for Itachi at that young age. A Sasuke vs Itachi fanfiction would be like a trigger for him. He would be eager to see how the fictional fight is portrayed. If Sasuke in the fanfiction is shown as strong, it might fuel his own ego and make him strive even harder to become powerful. However, if the fanfiction shows Itachi as superior, it could enrage him. He might feel that it undermines his own goal of defeating Itachi and he might even want to find the writer to correct their 'wrong' view.