Earth/Krypton's destruction really didn't matter.
Humanity had colonized all 9 (at the time of the graphic novel's writing, Pluto was a planet) planets thousands of years previously. It's likely that we had left our solar system long after, and we'd already gone into the afterlife (why someone didn't start having Luthor help is beyond this troper). So yes, humanity's homeworld was gone, but in it's place is a human empire.
- All the same, it's a pretty big loss of life.
- Lose of the galaxies governments check the destruction of the birthplace of humanity check and the loss of the worlds most brilliant minds and im pretty sure the earth was the elite of the world holding on the best and brightest minds and its all lost
'Verse is in this universe.
Luthor decided to make a Plan B, building tons of spaceships and sending them out to colonize another solar system far away from Earth. Over time, the story morphed into one of Earth's resources being used up and them leaving. Luthor had an affair with a psychic, creating the Tam line.
The baby that was sent back in time isn't going to become Superman, he's the russian Batman.
Gotham is part of the U.S.A. so why would Batman's origin happen in russia? As an extra theory, Gothams Bruce Wayne never became Batman here because of the events happening in America at the time.
Jordan Luth became the first person to travel to the afterlife. Over time this achievement was used to banish criminals and the dimension travelled to became known as the Phantom Zone