From PR-Inside:
Sarah Palin:40% Chance to Take Over as President // McCain Has Only 80% Odds of Living Out A Presidency
The chances that Vice President Sarah Palin would have to take over from President John McCain if they were elected could be as high as 40%, since McCain has about a 20% chance of dying in office, and a much higher risk of becoming disabled from a variety of conditions, including a stroke or Alzheimer's, both diseases which can impair judgment and where the risks increase very rapidly with age, notes Professor John Banzhaf of George Washington University.