i see vaders death as the same as sions, not only did the machines keep vader alive but also the dark side when he let it go to save Luke that was what did it. i mean when he asks Luke to take his mask off luke fears that will kill him which vader says "nothing can stop that now" which makes me think that yes his suit was damaged but combined with him letting go of the dark side he was no longer saving himself from the brink of death.
on a side not i find it funny that he could pick up a grown man with only one hand.
Vader was pretty much living off of the Dark Side. The life support systems kept him alive, but the Dark Side kept him going. Once he was redeemed, he died because he let go of the Dark Side and acknowledged and accepted his death.