I don't think his lifespan matters. I think spending years trapped in a petrified state without food, water, air, or sunlight would weaken Seto to such a state that if they used Supersoft to free him, he would soon die. Well, at least he'd be able to have a father-son moment with NanaRed.

By the way, I've come to a conclusion of what species red most closely resembles for us Earthlings. The cougar can vary in coat color from "pale buff" to "reddish-brown", it's about the same size as Nanaki and has a face to match. The only thing that's missing is the odd hairdo... and the ability to speak. I don't think cougars even roar.