Oh, duh! *smacks my forehead* That's right, heartless do have hearts. So, it would be given another non-corrupted heart? Man...I think Nomura screwed us over with a little hole there. But then again, a lot of things don't make sense in the KH series. Not that it's important or anything, but I actually have a list of them.
It's a play on words, Nommy likes to confuse us :lol:
-One being: After Mickey and Kairi were trapped behind the door, after Sora & Riku did all these leaps and battles to get to the very top; in the end of it all, how the heck did Kairi and Mickey end up at the top of the tower with Sora and co?
They were just behind the door, that's really all that there is to it.