[Roa_Aoife]

I guess to sort of restate what Farael is saying: holding a physical body takes a great deal of energy. It's about fighting entropy, which is the natural desire of all matter to be evening spread through out the universe. The fight against entropy is why we require things like food and water, etc. It takes energy.

Now Sauron, being one of the Maiar, had enough power on his own initially to hold a physical form with out any help or energy source. However, when he made the Ring, he poured almost all of his power into it and used it as his energy source, if you will. With out this energy source, he no longer had the power to fight the entropy, and his physical form vanished, like a high energy star turning to a black hole or going nova. So it was the loss of the ring that "killed" him, not the previous blows.

While I do think that Elendil and Gil-galad set up Sauron and weakened him, giving Isildur the chance to remove the ring, I don't think they "killed" him. It isn't like Isildur ran up and yelled, "Finders, Keepers!" and took the ring. He had some honor still at that point. I'm certain there was a strugle involved. As bilbo_baggins, Isildur was a warrior, a highly skilled one. That should be taken into account.