Wonder Woman was the first hero to appear in this universeIn Real Life and in the DC universe superpowered beings are called "superheroes" because Superman was the first one to show up. Now, in this universe, superheroes are instead called "Wonders", suggesting that Wonder Woman was the first one.
Superman is not really dead.Superman survived the trip through the Boom Tube and landed on Apokolips, where Darkseid is turning him into a weapon for future use. Mercury said something worse than Apokolips is coming, and what's worse than Darkseid? An evil Superman.
The lineup for a new Big Three.Based on what I've read, if Supes, Wondy, and Bats never come back, the main three on this world to replace them will be: Alan Scott: He has been claimed to be Earth's greatest champion and this troper believes that's what Superman is. Jay Garrick: Just as Wonder Woman was the avatar of the Greek/Roman pantheon, Jay will be as well. Kendra: She'll be the new Batman analogue by process of elimination.
Icicle will show up as a frost elemental.Now that Alan is an avatar of life and plants, it makes sense for one of his classic rogues to be similarly reinvented as an elemental with the power of death-bringing cold.