10 Immortal Comic Characters (Who Actually Died)
2. Death - The Thanos Imperative #3
Seeing Death itself die is a pretty big deal - especially in the Marvel universe, where figures like Jean Grey are dying and being revived so often you'd presume Death would have a revolving door installed in the afterlife. This likely explains why we never see Death die in the main universe, but instead in Earth-10011, charmingly nicknamed the 'Cancerverse'.
The Cancerverse is named as such because - in order to try and prevent the death of their universe's Captain Mar-Vell - the assorted heroes perform a ritual that kills Death itself in their universe, meaning the characters within this world are fated to live forever.
While this initially sounds pretty swell, the ritual also brings the evil Old Gods named the Many-Angled Ones into the universe, who immediately corrupted the world's inhabitants, messing them up beyond belief.
Essentially, the death of Death leads to the sort of nightmarish horror-scape that Lovecraft would consider a wet dream, and nobody should be all that surprised.