OK, I'm throwing out ideas here, but the more I think about this one, the more I like it. So here's what we know:
* MX released his heart and took control of Terra's body
* At least a part of Terra remained with the body - we can see that in Blank Points
* About a year later AX released his heart again, splitting himself in two - a heartless and a Nobody
* When a Nobody is defeated, the body goes to darkness
* If the heartless is defeated before the Nobody, and possibly vice versa, the heart and body will merge and the person returns.
So when Sora defeated Ansem SoD, the heart (or hearts more likely) went to the Org's Kingdom hearts which most likely started by that point. When the hearts in Kingdom Hearts were freed, I think that the universe "righted" itself and MX's heart went back to MX's body. But Xemnas was also defeated, making Terra's heart and body free. There is a very real chance that Terra have come back during DDD.
OK, I'm throwing out ideas here, but the more I think about this one, the more I like it. So here's what we know:
* MX released his heart and took control of Terra's body
* At least a part of Terra remained with the body - we can see that in Blank Points
* About a year later AX released his heart again, splitting himself in two - a heartless and a Nobody
* When a Nobody is defeated, the body goes to darkness
* If the heartless is defeated before the Nobody, and possibly vice versa, the heart and body will merge and the person returns.
So when Sora defeated Ansem SoD, the heart (or hearts more likely) went to the Org's Kingdom hearts which most likely started by that point. When the hearts in Kingdom Hearts were freed, I think that the universe "righted" itself and MX's heart went back to MX's body. But Xemnas was also defeated, making Terra's heart and body free. There is a very real chance that Terra have come back during DDD.