Director's Secret Report XIII

[PuPu]

Just because the other characters have fused with their other side it doesn't mean Xemnas just needed to fuse with "Ansem". Also there would still be a missing part: The body.

Read this part of the DSR13:

When heartless are defeated, essentially the owner's hearts are rejoined with their once extinguished body, whichever world it may be on...In the case of a Nobody being defeated, it's a little more complicated. If the above mentioned hearts are liberated, they return to their original form.

Xemnas and XH both disappear simultaneously, then we have Xehanort again.

And it still does not matter. Ansem (while controlling Riku, not Riku who just looks like him but has his own will) and Xemnas have never met. So they never had the chance to fuse even if it would work.

You're right about one thing, it doesn't matter for AnsemSoD. He never said anything about being whole again. However, Xemnas definitely had the opportunity. Xemnas has been watching Sora since KH1, and he would have definitely known that Sora was fighting with AnsemSoD and could definitely have the opportunity to fuse.

Also I do not believe Roxas really has emotions just because he is "special".

Roxas cried. Roxas got extremely angry. As a result of said anger and sadness, he went off to try and do an extremely stupid thing before he was stopped by Riku.

Naminé and Axel also have emotions too, FYI.

You can see emotions of almost everyone in the Organization XIII because Nobodies just act like they would have feelings and because it is difficult to make a whole story with boring, emotionless characters.

The difference is that all the other Organization members show emotion as a ruse, but don't feel emotion. You can tell because these emotions that they show don't affect their actions in any way.

if Mickey's Kingdom Key of Darkness cannot defeat bosses in the Realm of Light

This is another gameplay element that is not related to the plot.