Just stumbled across a couple of 'Naruto is dead' fics that really messed with my head. There's one where he dies during the Chuunin Exams and it's like a cold case investigation fic from Kakashi's POV, which is a mood I didn't know I needed. The author spends so much time on the aftermath—how the village slowly fractures without its loudest, most unifying presence. It's less about the death itself and more about the hollow space left behind.
Another one I keep thinking about is this weird, almost philosophical AU where Naruto's death is the inciting incident for Sasuke to completely reject the concept of ninja villages altogether. It turns into a road trip story with Sakura, of all people, trying to track him down. The writing can be clunky in spots, but the central idea of a world where the 'sun' goes out is haunting in a way most action-heavy fics aren't. I'm not even sure I 'enjoyed' it, but it stuck with me for days.
Most of the good ones I've found aren't actually tagged as major character death upfront, which is annoying. You have to dig through angst tags and post-war fics. The real standout for me was a time-loop story where Sasuke is the one trapped, forced to relive the news of Naruto's death over and over, each loop revealing a different consequence. It's brutal, but the character study is impeccable.