Based on Speculations and Observations

 

In KH2 when Ansem the Wises machine blew-up the whole area filled with light, hearts were raining down and Riku turned back to normal, mybe Xehanort was able to get one of those hearts without fully realizing it. Seeing as we all think the next game is Sora going out to rescue Ventus, Aqua, etc., this would make it possible for Sora to rescue Terra. He wouldn't have been destroyed at the end of KH2 just sent into the relm of darkness like Sora, Riku, Ansem, and Aqua were.

Well Xehanort's heart was fused with Terra's, and so when the machine exploded, I guess the two hearts could have spilt up once again and become their respective hearts once more.

Terra's heart is in a similar state as Ven's, since his, Master Xehanort's, and Eraqus' heart have merged together and went on to become Ansem SoD.

 

Also, when a person's Heartless and Nobody are defeated, it becomes possible for the Somebody to return, and if they do, they do so on the world they first lost their heart on, meaning, if Xehanort the Apprentice has returned, he'll be on Radiant Garden.

 

Since Ansem SoD was defeated first, the heart of Xehanort the Apprentice was left in a state of suspension, waiting for his body and soul so the complete being could be reborn.

yeah if there hearts split then where is terra's heart?

This is a good theory, but there are 2 reasons this couldn't have happened

1. The real Xehanort, the full one, is currently nowhere to be found, assumed dead.

2. If he was alive at the time, he wasn't in the World that Never Was, where the heart shower occurred.

There is a possibility... although I'm not sure, one part of me says that in the explosion, Terra's heart, separatedly from MX's, returned but to Lingering Sentiment because his body is gone; but another part of me says, it can't be, because the heart shower only occured in The World that Never Was.

 

There are so many possibilities as how Sora can save Terra.

I think the rebirth of Terra will defitently happen! Plus I will be really glad when it happens!

it will definitely be interesting to see what happens with Terra/Xehanort. i agree that the raining hearts thing took place only in TWTNW, so that wouldn't have brought Terranort back. but if Sora can get him back some other way, along with Ven, Aqua, etc., and separate MX's heart to bring him back, it would be interesting to see what would happen with more keyblade wielders going after MX now. this time you would have Terra (maybe), Ven, Aqua, Sora, Riku, perhaps King Mickey, Kairi, maybe? (big if there), and if Sora "rescues" her, Xion may take part in the fight. there would be up to eight keyblade bearers there, going against just one (MX). lots of speculation here.

it's gotta happen or the story of xehanort will not end and they will not have an idea for kh3? :[