He's dead and gone - he outright tells you before the battle he was fully intending on burning through his entire aether, life and soul to go head on with the WoL (the WoL does pretty much the same thing). He consumed it all, and by the end, had nothing left (when the WoL finally knocks him down).

Only the WoL is saved by a deus ex machina, leaving Zenos dead, reviled and unmourned on the edge of the universe. Good riddance to the crazy stalker and his stupid prettyboy hair.