JKR has been "gently" preparing us for his demise for a while now. So though we'll be sad, we'll also say, "Well, he was *old,* after all..."
The dreaded cliche I hope we never get to see:
Voldy and Dumbledore in a Battle to the Death! Dumbledore takes a mortal blow, falls into Harry's arms, utters some profound secret to Harry, and dies. And whatever he said/having Dumbledore die is just the LAST STRAW for Harry, and he blasts Voldy into neutrino and quark dust.
But I have a feeling Dumbledore might last longer than anyone else, and be involved in Voldy's demise somehow. (can you say....DUH?)