Superman in past tense
Gimme a break. Unless Otis slipped kryptonite into Clark's coffee somehow Superman is immortal & mostly indestructible & airworthy.
HOW would Superman keel over anyway?
What became of Superman you ask?
He lived eternally everafter, frustrated by the deaths of his loved ones, friends, lovers, aquaintances, even his adversaries.
And how did/does Superman fake the passing of Clark Kent?