What if Aqua was around, though..? If Braig was the little devil on Terra-Xehanort’s shoulder, Aqua would have surely been the opposing angel, and I’m positive that Aqua and Braig would have clashed many more times as a result. She already knew he was working with Xehanort after fighting him in the Keyblade Graveyard, and with certain revelations about who Braig really is, he certainly had machinations of his own that Aqua would have stood in the way of.

Would Terra-Xehanort have still betrayed Ansem despite Aqua’s influence around him, thus causing the events of KH1 and KH2? Maybe, maybe not. Her escaping the Realm of Darkness immediately would have also placed her in Radiant Garden -- in Kairi’s home. They surely would have met again and again, and maybe, just maybe, Aqua would have taken her on as an apprentice to train her in using the keyblade many many many years before she would have ended up training with Yen Sid and Merlin. 

Ventus, Sora, and Riku would all be factors, too. Would Aqua visit the latter two on the Destiny Islands, or would her clashes with Braig and desire to restore Terra’s memories keep her around Radiant Garden? Would she have found a way to mend Ven’s heart and wake him up with the aid of Ansem’s research, or would they have still needed Sora to fill in that missing piece?