Considering this is FF4 expansion & Zenos is fairly identical to a certain Goldbez I too doubt he is actually dead. Also we know Zenos can't control his resurrection as even he was surprised to live in SB & based on Reaper questline it feels like he would've you know exploded into void dust like the Reaper Job quest, I fully expect a Goldbez turn with him changing & becoming a kinder good guy.

Still la lot of mystery around Zenos such as what experiments did Varis do to him when talked about Zenos being nothing but a Experiment/monster or Fan Daniel talk about whatever Emet may have done to Zenos "could Emet found a way?" plenty of stuff to delve into with Zenos. 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.