1.The world ends. Society collapses into a new dark age.
2. Superman escapes a doomed earth in his rocket.
3. Earth-1 is introduced. (It's not quite what you'd expect.) Barry Allen of Earth-1 dies in the Crisis.
4. Kal-L returns. JSA/JSA.
5. End with Superboy-Prime "going home" powerless. He's locked in an institution ala Psycho Pirate in COIE screaming about how there are INFINITE earths as we pan out to see them. Exact opposite of COIE ending.