In this kind of fanfiction, Sasuke could die from a sneak attack. He might be so focused on his main target during the Wave mission that he doesn't notice another hidden threat. And this hidden enemy could strike him when he least expects it, leading to his death. For example, an assassin could be hired to specifically target Sasuke and use some sort of poison or a deadly jutsu that he can't defend against in time.
Glenn meets his demise in the comics during a particularly intense and chaotic event. The circumstances surrounding it are quite harrowing and have a significant impact on the story's direction.
Negan's death in the comics occurs at a specific point, but I can't recall exactly when off the top of my head. You might need to do a detailed search or refer to dedicated comic forums for the precise moment.