I'm unsure if your referring to Xion or Zexion, so I'll answer both, I guess.
Zexion was the nobody of Ienzo. After Dream Drop Distance, Ienzo was revived as a human. So while Zexion can't come back unless Ienzo loses his heart again, the two are literally the same people.
Xion was a replica created by Vexen by using Sora's memories of Kairi. I'm not sure, but I believe Namine cleaned up all of Sora's scattered memories, so I think the rebirth of Xion is impossible. Plus, there's also the possibility of Even not being able to do the experiments Vexen carried out, but that's highly unlikely. So probably no for both, sadly. :(