I'm bad at writing... but here goes!
The Homeworld gems have started colonizing on, Earth rapidly reducing life on it as they start to hollow out the world. The rebellion has failed, leading to the deaths of Pearl, Garnet, Amethyst, and Steven. And in their deaths causes a riot within Beach City. The older, now more mature, Connie rises into power as she strives to defeat the Homeworld gems in vengeance for the fours death and to save the earth. Now both humans and few sympathizing gems strive to save the earth from the impending doom.
Edit:
The Homeworld Gems start to take over many cities of Earth. Destroying them and building warp pads over the remains and soon taking over each government and totally obliterating what's left of humankind.
That's... my idea? Connie would be about twenty in this plot and, Steven's dad would be somewhere? Any ideas?