Well, it was mentioned that in KH2, in this room called the Proof of Existence, it has name plaques/tombstone things for all Org XIII members. They glow red if the member is dead, and blue if they're alive. Zexion's is blue. At least, she thinks she remembers it was. Could be an animation mistake, but it's much more interesting to think it wasn't! She said she'd try to double-check that and see if she was remembering right.