Spider-Man: in an embroiled super-battle, some punk decideds to "Help" and gets off a lucky shot.
Dr. Strange: a disease has been eating at him for years, he has kept this hidden, but now he must choose a successor or risk the title of "Scorcerer Supreme" falling to Dr. Doom.
Dr. Doom: aw screw it, this guy's to stubborn to really die. or if it does happens... I want it to be at the claws... of Squirrel Girl!
Galactus: near end of time, he has been slowly starving to death for decades and is preparing to pass on. his last herald, Craig "The Immortal" Hollis, comforts the Big G as he passes on.
Hulk: Banner, in a fit of depression and desperation decides to destroy what he believes is the greatest threat to the universe: himself. he commits suicide by ODing on tranquilizers.
Captain America: he recieves a fatal wounds, but wins the battle, as Peter Parker holds him, trying to get him to a hospital, Cap demands they land. there, Steve gives Peter the shield, telling him to take it and lead them (the avengers).
Iron Man: Alcohol poisoning brought on by binge drinking after everyone drops his bum ass for playing them during the civil war.
Cyclops: infected with a brood egg, He begs the X-men to kill him before this brood queen hatches. most shy away, but Wolverine steps forward. as he guts Scott, Logan says "Y'er All right."
Shocker: Shultz accidently kills a kid as he's fighting Spider-Man. the headline goes up "Shocker: baby killer" unable to live with the guilt, Shultz hangs himself in his jail cell.
Mystique: a group has been secretly gathering strength to attack the mansion, too strong for the X-Men and their passifistic ways. Mystique steps in front of them as they are on their way. "You can't stop us mutie," the leader snarls. "I know," she replies, "I don't need to though. I just need to thin you out."