He didn't say they were traveling somewhere either:

Maduin: Terra... We must part now. We espers will disappear from this world. You may fade away as well...
Maduin: But perhaps if the human part of you feels something strong enough , then maybe... just maybe you will be able to remain here as a human.
Considering the Magicite you have is literally turning to dust in your party's hand. I would say that killing the Warring Triad took out the remaining espers and their magicite as well. Hell, in an old V-Jump interview, the Kitase, Sakaguchi, and Saga, revealed that Terra was meant to share the fate of the espers but decided that was going too far and didn't want to give the game a downer ending, so they gave her a Disney Death instead. So I would say, that "disappear" and "fade" in this context means to cease to exist.

So in order for an FFVI sequel to have magic, they would need a new set of beings like the Warring Triad.