I don't know... I could swear I read somewhere that if a person loses his heart and becomes a Heartless and a Nobody, he will be back to normal if you first kill the Heartless and then the Nobody. But I can't remember where I read it or if this is true. I know Axel is back in Kingdom Hearts 3D as his real self Lea, well at least according to the trailers. So there must be a way for Nobodies to be back to normal.
*sigh*
I wish I had a 3DS and KH 3D, then maybe I would know...