- It's hard to imagine how there could ever be a sequel. With magic ceasing to exist completely, and the world still being in a mostly-ruined state at the end, I don't know what else there would be that could sustain a whole game's worth of plot. Almost certainly for the best to simply leave it there and not try to revisit it. That said, I do wish the ending cutscenes had given some idea what the characters were going to do with themselves afterwards, as FF4 and FF5 did. The scenes of them escaping from the collapsing tower were cute, but this probably would have been a bit more satisfying. Ah well.
A prequel which takes place during the war 1000 year ago would be easy. A sequel is possible too, as we only see three gods who made a mess with the Earth, who knows how many others are out there. Just need to say the power of those three shielded the Earth from the others and now Earth is open to new comers to take over and we can build up a story that permanently resolve this problem.