Death for Elves and Men (and Dwarves, I guess) means leaving Middle Earth for
another place, either to stay in Mandos to be reincarnated (or in Durin's case,
reanimated)or pass away altogether. But for Maia, who are native to Valinor and
are more hallowed than the Vanyar, being killed in incarnate form is near
impossible. Sauron was defeated by the loss of his own power into the Ring, and
his anchor (his bodily form) cut loose, sending him into nothingness.
Gandalf died from the sheer effort of killing the Balrog, and his spirit was
practically e-mailed to Iluvatar for assessment. Of course, he was in the body
of an old man, and not Olorin the mighty.
Saruman is another "?" point. He has lost his powers and staff, and with it any
skill he had as Curunir. When he gets killed, his spirit looks West and is then
blown away. This might be something worse than death-Saruman is still alive but
unable to communicate with anyone and unable to move anything. He is quite
literally a lost
soul.
There is but one task remaining in Arda-we,the Dragons of Valinor will make it happen.
Lone resident of the Republic of Gondor
PO-TA-TOE-S not PO -TAH-TOE-S!