If Square leaves a game open ended, I don't see the problem in making a sequel if they want. FFX-2 was really awesome, despite everything bad everyone thought about it before it came out. I'm sure FF7:AC will be cool too. That being said, FF8 ended the story quite well. I can see a few ways they could bring the story back, but I don't think anyone is really expecting the story to continue, it was a very nice satisfying ending. So I personally don't see Square even thinking of doing a sequel to FF8. But with the massive success of FFX-2 (1.9 millions copies sold in 1 day!!!) and the probable success of FF7:AC, I would anticipate sequels in Square's future, hopefully not too many though, I do like new games.