John McCain is 72 and actuarially has a higher risk of dying in office than a younger man. But he is in good health (he’s released over 1,000 pages of his medical records; Obama, with typical parsimony, has released one page) and 72 is a good deal younger than it was in earlier times. He is hardly likely to shuffle off this mortal coil immediately after the inauguration.
Out of 43 presidencies, only two ended in the very early days of the administration. William Henry Harrison, age 70, took the oath of office on March 4th, 1841, gave the longest inaugural address in the history of the Republic, caught pneumonia as a result, and died a month later. (Joe Biden might want to note this example of the hazards of oratorical prolixity.) James Garfield, age 49, took the oath on March 4th, 1881, and was shot by an assassin on July 2 that year. He lingered for two and a half months until his incompetent doctors finally managed to kill him.
With modern medicine, both Harrison and Garfield would have been back at work within two weeks.
The fact is, if John McCain were to die after only a year in office, Vice President Sarah Palin would have more foreign policy experience, by far, upon entering the presidency, than four of the last five presidents, who were, like her, all governors and had never held federal office.