John McCain would be 72 if assumes the presidency. What is the probability that he will die before he finishes his first term?  The proper way to estimate the probability McCain would die in office is to use mortality rates of people at his age. The most current and authoritative data I found are published by the Human Mortality Database at www.mortality.org sponsored by the University of California, Berkeley and Max Planck Institute for Demographic Research

Using their 2005 data, (you have to register to use it), three percent of 72-year-old men died before their 73^rd birthday.  Using the numbers for each year for four years, 86% of current 72-year-olds would still be alive at their 76^th birthday, the end of one term. Eighty-two percent of them would not die before the first year of a second term. That means the probability of a 72-year-old man dying within five years is 18%, or about one in fivefour. This is roughly equivalent to flipping a coin two times and getting “tails, you lose” both times. 

McCain is aged. Reporters have noted his confusion and he has displayed it when talking about Muslim sects while in Iraq. The Wall Street Journal reports his Republican handlers eliminated his impromptu open bus interviews with reporters.  Handlers have reduced his open press conferences.  He read a written statement on Georgia, which is touted as evidence of his foreign policy expertise. However, after he read it he refused to answer questions and immediately walked away from the microphone without acknowledging who wrote it.