Her FutureAfter sacrificing herself to save Terra's body, Aqua fell into the Realm of Darkness. Since then, she has been wandering around aimlessly for what seemed to be forever. To make matters worse, she was completely alone. Driven by nothing other than knowing she had to be reunited with Terra and Ven again someday, she eventually comes across Ansem on the shores of a beach. Aqua, never seeing anyone other than herself, begins to converse with him. He does not remember much about who he is, but he does inform her that the worlds in the Realm of Light are in danger. Even so, there is a boy fighting to save them. Listening to his story, Aqua finds out that it has been at least ten years since she has been wandering and is hopeful that the boy fighting the darkness with a Keyblade is Terra or Ven. Her disappointment that neither of them are the boy is short lived. When she hears that Sora is fighting to save the worlds she is hit by a wave of hope and happiness. So much so that she begins to cry. She had met Sora and Riku on Destiny Islands ten years before and I would assume just knew that the worlds were in good hands. Not only that, but Sora would be able to save her and her friends.
Aqua appears once more in the secret ending of Dream Drop Distance; still hopeful as she looks over the dark waves on the same shore she met Ansem. I personally believe that the time is nearing that she will be saved by Sora. In the secret ending to Birth by Sleep that I described above, when Ansem tells Aqua that Sora is the boy fighting to save the worlds, all the characters who have met a tragic "end" say his name: Naminé, Roxas, Axel, Xion, Terra, Ven and finally herself. The E3 trailer for Kingdom Hearts III has Sora telling Riku that he's made up his mind to go help the people who have made him who he is today. All of the characters that said his name are connected to Sora's heart in some fashion. He is also clutching the note from King Mickey that he received at the end of Kingdom Hearts II. In a previous game, Mickey has made reference to knowing where Ven and Aqua are and that they just needed to locate Terra in order to save him as well. In addition, Yen Sid discusses an upcoming war between thirteen darknesses and seven lights at the end of Dream Drop Distance. Sora, Riku, Kairi and Mickey are only four. If they rescued Terra, Ven and Aqua, they would have seven Keyblade wielders. Naturally this is all only speculation right now, but I am hopeful that the Wayfinder trio will finally be rescued in the upcoming Kingdom Hearts III.
More information will be added to this section as we learn more about the game!