Zenos is... [big fat spoily]

[Enkidoh]

Also what's with people assuming he used up all the mother crystal energy to get there/fight us he may still have reserves & even if that is the case I imagine he can easily control all the Dynamis in that zone.

Zenos consumed what was left of the Mothercrystal to turn into Shinryu and to travel to the Dead Ends - and that he needed to use every last drop of aether it gave to do so (notice he actually did not help the WoL with the Endsinger but merely acted as a stage for the fight?) - remember the Ragnarok needed to use up most of the Mothercrystal to do the same thing.

And afterwards, Zenos himself outright tells you that "he will have to burn through the candle of his life" to face the WoL, he was basically saying then and there "this will end me, but as long as I get my glorious battle with you, then I will die happy." And that is exactly what happens. He might have had some left over 'Mothercrystal' aether within his body for his last battle, but I pretty much doubt it.

The fact SE actually had him state that made it pretty clear that is exactly what takes place, it's pretty clear cut. He's gone and is not coming back.