I wonder if the sun becoming a red giant was what caused the god kids to abandon the earth for Caliborn/Caliope to inhabit later

It’s hard to say. As I’ve mentioned before, there’s also the chance Calliope and Caliborn weren’t born in one of the Timelines we’ve seen- Karkat, Dave and Jade dig up the Liberties, so there’s a chance the fact there’re so many of them in the Cherub World implies the Kids didn’t really. Win? Maybe it’s a Condy Wins Timeline- We do see a Troll off-world colony, and if they had stayed underwater still, it’d explains the Liberties being everywhere.