Even Mxy has commented on the fact that not only does some version of Superman exist in every Universe in DC, but should he be killed/destroyed that Universe is thrown out of balance, and experiences an Armageddon of sorts.
Anyhow...
Superman is without question DC's ultimate hero, and thus will always be around, and thus will always have a "higher" purpose...
__________________
"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."