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 and can only be cured by leaving the current area. Characters can cast Warp or use Warp Motes on enemies to generate a similar effect.