Edea never gets possessed?
*Thinks for a minute*
Well, first of all, the parade would have never been and we would have lost a great song (Fithos Lusec Wecos Vinosec).
Second, SeeD would be out of a job unless Adel somehow got freed or Rinoa got powers somehow. (Unlikely in either aspect)
Third, and I think foremost, there never would have been the big break between Seifer and Squall. They would have just been rivals for the rest of their lives, always fighting over the same girl.
Of course, that's if you really take it in the context of the story. I personally think that Cid and Edea would have eventually come to blows. She takes Galbadia and he takes Balamb, and they have a nice little WWIII between the two schools. All over which side of the plate the little fork is supposed to go on.
Alright, for mine. What if Squall had actually been able to summon Griever himself?