This is Oblivion's Comprehensive THEORY guide on the possibilites of returning characters. Spoilers are included.
RETURNING CHARACTERS:
.01%- Marluxia: This is because theres absolutely no reason to bring him back; he tried to kill Sora, tortured Namine, and the entire Organization knows he is a traitor. No plot threads could come from him. Unless Nomura decides to bring the entire Organization back, Marly is gonna stay dead.
.01%- Larxene: Same reasons as Marluxia. She teamed up with him, and Sora hates her guts. If she comes back someones gonna reverse it quickly.
10%-Lexeaus: He really doesn't have a big role in any game, but he might come back, just because he might have a glorious role to play. He is the "silent hero" after all...
10%- Xaldin: He might have something to do too, but I still don't think it's likely he will return, mostly because there isn't much he'd be useful for plot-wise.
20%- Ansem the Wise: He went out in style for his mistakes, and frankly, he isn't really needed anymore.
25%-Vexen: He's a brilliant damn scientist, so he knows alot about the inner workings of what the organization's experiments were. He's also a coward, though, so he might not return for that reason.
35%- Zexion: As Vexen's aide, he has much the same reasons as Vexen; however, he's a popular character, his weapon was never really used much, and he's extremely crafty, so he'd introduce alot of plausible plot threads.
35%- Vanitas: Much as I hate to say it, Vanitas doesn't have alot more business to take care of among the living. He's probably gone for good, but say his lingering spirit starts to haunt someone... or Nomura wants someone of the old crowd to spice things up for Sora (imagine him seeing Vanita's face!) If Ventus's heart gets restored, it's safe to say thats the easiest excuse for him to come back.
35%- Master Eraqus: He should be gone for good, but he might just make it back to teach Sora ancient ways of the keyblades, and possibly make Sora a keyblade master.
45%- Demyx: He's a little cowardly, and serves almost no purpose, but he's lovable, and we all know he's harmless. If he returns, he'll probably join with Sora and Co.
50%- Luxord: He has even odds of returning; he never really had such a big role, but, being the expert gambler he is, he knows how to pick sides to his advantage, so he could be either bad or good. With his luck, he might just make it back...
65%- Xion: Now, I really don't think she has any business turning up again, but she really didn't do anything to deserve her banishment, and she's a good character. Nomura might just go with the "happy everybody lives" ending.
70%-Xehanort: His old body may have been destroyed, but if Terra gets free of him, you can bet he'll want revenge. He's a crafty keyblade master, has ancient knowledge, and if Vanitas can have a spirit hanging around, Xehanort certainly can.
90%-Roxas: He's technically still alive, but I'm talking about living separately from Sora. He'll fnd a way to live apart from Sora, and find Axel, and spend his days eating ice cream again, maybe even with Xion.
90%-Namine: Same reasons as Roxas, and because she has power over memories, which is useful. She could possibly be the one to unearth Sora's memory of meeting Ven.
95%-Terra:I think its safe to say Terra will come back, to make up with his friends one last time. Even so, it might just be too late for him, so his odds are not positive.
100%- Axel: Axel is most certainly going to have his last word, as always. He will return, since Nomura has stated he wants Axel to anyways, and reunite with either Roxas, or, if thats not possible, Sora.
100%- Saix: If Nomura has any good points, its his promise to, sooner or later, explain everything. Bringing Saix back, he can explain his and Axel's frienship further, how they plotted against the organization, how they started hating each other, and, lastly, they will become friends again, because that is how Kingdom Hearts works.
100%-Master Aqua: She made a damn promise, and she isn't evenb truly dead, and its high time she got out of the dark realm. She and her friends will be together once more if its the last thing she does.Because she's a motherfiretrucking keyblade MASTER.
100%-Ventus: He is the X-blade, he is integral to the upcoming storyline, and he is closer than ever to getting his heart back; Sora is getting close. Aqua will see that her promise is fufillied.
101%-Xigbar: He knows more about everything than anyone else, and his motives and complete knowledge have not yet been revealed. I consider him the most dangerous Organization member; he knows more about Xemnas than Xemnas himself does. At one point, it almost seemed like Xigbar was a good guy, but be wary of him. He hasn't had his final say yet, and you can bet he'll get it.
This is Oblivion's Comprehensive THEORY guide on the possibilites of returning characters. Spoilers are included.
RETURNING CHARACTERS:
.01%- Marluxia: This is because theres absolutely no reason to bring him back; he tried to kill Sora, tortured Namine, and the entire Organization knows he is a traitor. No plot threads could come from him. Unless Nomura decides to bring the entire Organization back, Marly is gonna stay dead.
.01%- Larxene: Same reasons as Marluxia. She teamed up with him, and Sora hates her guts. If she comes back someones gonna reverse it quickly.
10%-Lexeaus: He really doesn't have a big role in any game, but he might come back, just because he might have a glorious role to play. He is the "silent hero" after all...
10%- Xaldin: He might have something to do too, but I still don't think it's likely he will return, mostly because there isn't much he'd be useful for plot-wise.
20%- Ansem the Wise: He went out in style for his mistakes, and frankly, he isn't really needed anymore.
25%-Vexen: He's a brilliant damn scientist, so he knows alot about the inner workings of what the organization's experiments were. He's also a coward, though, so he might not return for that reason.
35%- Zexion: As Vexen's aide, he has much the same reasons as Vexen; however, he's a popular character, his weapon was never really used much, and he's extremely crafty, so he'd introduce alot of plausible plot threads.
35%- Vanitas: Much as I hate to say it, Vanitas doesn't have alot more business to take care of among the living. He's probably gone for good, but say his lingering spirit starts to haunt someone... or Nomura wants someone of the old crowd to spice things up for Sora (imagine him seeing Vanita's face!) If Ventus's heart gets restored, it's safe to say thats the easiest excuse for him to come back.
35%- Master Eraqus: He should be gone for good, but he might just make it back to teach Sora ancient ways of the keyblades, and possibly make Sora a keyblade master.
45%- Demyx: He's a little cowardly, and serves almost no purpose, but he's lovable, and we all know he's harmless. If he returns, he'll probably join with Sora and Co.
50%- Luxord: He has even odds of returning; he never really had such a big role, but, being the expert gambler he is, he knows how to pick sides to his advantage, so he could be either bad or good. With his luck, he might just make it back...
65%- Xion: Now, I really don't think she has any business turning up again, but she really didn't do anything to deserve her banishment, and she's a good character. Nomura might just go with the "happy everybody lives" ending.
70%-Xehanort: His old body may have been destroyed, but if Terra gets free of him, you can bet he'll want revenge. He's a crafty keyblade master, has ancient knowledge, and if Vanitas can have a spirit hanging around, Xehanort certainly can.
90%-Roxas: He's technically still alive, but I'm talking about living separately from Sora. He'll fnd a way to live apart from Sora, and find Axel, and spend his days eating ice cream again, maybe even with Xion.
90%-Namine: Same reasons as Roxas, and because she has power over memories, which is useful. She could possibly be the one to unearth Sora's memory of meeting Ven.
95%-Terra:I think its safe to say Terra will come back, to make up with his friends one last time. Even so, it might just be too late for him, so his odds are not positive.
100%- Axel: Axel is most certainly going to have his last word, as always. He will return, since Nomura has stated he wants Axel to anyways, and reunite with either Roxas, or, if thats not possible, Sora.
100%- Saix: If Nomura has any good points, its his promise to, sooner or later, explain everything. Bringing Saix back, he can explain his and Axel's frienship further, how they plotted against the organization, how they started hating each other, and, lastly, they will become friends again, because that is how Kingdom Hearts works.
100%-Master Aqua: She made a damn promise, and she isn't evenb truly dead, and its high time she got out of the dark realm. She and her friends will be together once more if its the last thing she does.Because she's a motherfiretrucking keyblade MASTER.
100%-Ventus: He is the X-blade, he is integral to the upcoming storyline, and he is closer than ever to getting his heart back; Sora is getting close. Aqua will see that her promise is fufillied.
101%-Xigbar: He knows more about everything than anyone else, and his motives and complete knowledge have not yet been revealed. I consider him the most dangerous Organization member; he knows more about Xemnas than Xemnas himself does. At one point, it almost seemed like Xigbar was a good guy, but be wary of him. He hasn't had his final say yet, and you can bet he'll get it.