If you think Kuja....(Spoilers)

[Leon]

...destroyed Terra, you are right, but only to an extent. He may have destroyed Bran Bal and maybe Pandemonium, but he didn't destroy the entire planet. As in, like how Frieza destroyed Namek with his Death Ball in the DBZ anime/manga. Terra didn't seize to exist, because before you fight Deathguise, Kuja mentions that Terra had already begun to assimilate with Gaia. If it was completely destroyed, then how can nothingness assimilate with Gaia?

Had to point this out, because I even got a negative Thanks for pointing this out. I'll probably have a bunch of naysayers but please, do tell me how I'm wrong.

EDIT: There, changed the title a little. Sorry about that.

EDIT 2: Nvm, don't think I can change it.