On the face of it, one of the stronger arguments against McCain/Palin is that McCain is older than dirt and will likely keel over any second now, and that Palin is too inexperienced to take over when that happens.
So what is the likelihood that McCain does indeed shuffle off this mortal coil shortly after being elected? I'm surprised that I haven't seen this probability published in any of the dozens of articles that I've read that have made the above argument.
I looked up the relevant probabilities in the Social Security Administrations Actuarial Life Table. I don't think there is any information regarding McCain that would allow us to do better than these tables. Yes, he's had skin cancer and his ancestors have died somewhat younger than average. On the other hand, he looks reasonably fit, healthy, and vibrant, and I think that pushes him back towards having typical life expectancy. Maybe not, but it's still an interesting exercise to consider life expectancies for typical men of McCain's age.
From the tables, McCain has close to 97% probability of surviving the first year and better than 85% chance of surviving all four years. So no, he's not all that likely to kick the bucket during the next presidential term.
Another way of looking at it is this. If experience is critically important, and you consider McCain to be adequately experienced, but Obama only to be 80% likely to be adequately experienced for situations that might come up in the next four years, you'd be better off voting for McCain, even if you think that Palin certainly does not have adequate experience.