Well, this has been brought up before, but at least it isn't another case of trying to replace Namine's position with Xion, which can't be done because it's been said so many times, that Namine and Roxas were born at the same time. Anyways, I don't think this is true, but nice try anyways. There was no loss of heart or anything.. then again, who says Kairi's heart didn't temporarily leave her body in order to cleanse Sora's heart of darkness and therefore, bringing him back? Yes, even the KH universe might have it's limitations, but I'm pretty sure that there are still many unknowns out there. Along with the circumstances of Ansem's death, this might be one of them.
Note: I'm bringing up Ansem's death because there are chances, that he may not of actually died or not actually died the way we thought. We'll see in KH3 though.