The character has vanished without a trace. The effect cannot be reversed.
X-Zone is a negative status effect appearing only in Final Fantasy XII. It is only inflicted through Telega, a magick that only Demon Wall has access to. It casts one character into the Void, making that character disappear and unable to be controlled.
X-Zone lingers after battle but can only be cured by leaving the current area. Characters can inflict the X-Zone status effect on weaker enemies by casting Warp, or by using Warp Motes.