that last statement is agreeable... but who's to say they didn't want to become their old selves? I mean sure Xemnas probably had the intention of become a whole existance, but the 'whole existance would result in becoming this so-called new being, or result in Xehanort, Terranort or even Terra for that matter
Here ya go:
–The initial members of the Organization abandoned their hearts intentionally? Why, now, do they collect hearts?
Nomura: The reason is to have a ‘complete existence.’ KH1’s Ansem (Xehanort, stealing this name) had a purpose, and realizing that he had transcended being a human, turned into a Heartless. Xemnas remembers that purpose, but as a Nobody, ‘an empty shell,’ collects hearts to become complete. The other members of the Organization have their own expectations, but are there mainly for the purpose of collecting hearts to complete Kingdom Hearts, as only Xemnas stared ahead and made it a priority. It is natural that Nobodies, who do not have hearts, demand hearts, though it may seem that Sora’s defeating them is unnecessary, the Organization members don’t look for their own hearts, but collect many from unspecified persons, and use them instead, placing the hearts in a situation where they cannot go back to their origin.
The bold part spills it out word for word, the members
don't look for their
own hearts. They want to become a complete existence on
their terms, not become their old selves again.
But this is exactly what I'm talking about. It would cause irregularity in the fusion and make it an abomination beyond hope of salvation. The host wouldn't even be able to control it's actions. The darkness emanating from the heart would consume the body and transform it into something all-new and dangerous. This is exactly why I suggested this.
A fusion like that can't even happen because there
is no heart emanating darkness. The heartless itself is the darkness and there is no heart to function.
Okay, let me sum up what I'm trying to say. Were talking about a Nobody with no heart. And then we have a Heartless with someone else's heart. Hearts can change the appearance of each host. Also, this heart has already been taken over by darkness and isn't starting to sprout it inside the host, which was the result of Anti-Sora. You take that and put it into an empty vessel. And what do you know, you've got a being that looks like a deformed hybrid of two people while spewing darkness everywhere and having Heartless-like qualities of the type that's inside. Also, you're missing my point, the host DOESN'T have a griffon it's heart, the darkness does. Which will likely make it act like a savage and go on a rampage just like a mindless Heartless.
Hearts only change the appearance of a host when they're really there, a heartless
already is the being taken over by darkness. You can't take out the heart of the heartless without it going into the RoD and turning into a heartless right again except when slayed with a keyblade. But then the heart is purified and no longer consumed by darkness.
In that case, if no nobody was formed, the heart automatically starts to search for its body and the original person is eventually reborn.
If a nobody was born and it is still around the purified heart goes into a state of suspension, waiting for the nobody to be slain so it isn't "occupying" the body anymore.
If the nobody was already slain before the heart also starts to look for it's body, and depending on how long the nobody was slain before the original self may return as well.
The only irregular things happening that prevented exactly this circle were in KH Days and KH II when Organization XIII intercepted and captured those purfied (freed) hearts to make their own Kingdom Hearts.
That is a logical error in itself, if the "host" (meaning the body+soul) doesn't have a grip on the heart because of
darkness, the heart will immediately leave the body again and form a new heartless.