I was at the Smithsonian Air and Space Museum this weekend and they had an exhibit with an old vending machine that used to be in airports that for one quarter would sell you $7,500 worth of life insurance that would cover you in case your plane crashed (pictured here). A quick calculation shows that for the insurance company to make money planes would have to have fatal crashes in less than 1 in 30,000 cases. This source suggests in the 1960s crash rates were 1.2 out of 100,000 when these machines were popular.
However, this assumes that someone buying insurance will not influence the probability of a fatal crash. In researching these machines, I found the story of United Flight 629, which was bombed by the son of one of the passengers who had purchased extra insurance at the airport for his mother's trip.
So perhaps that's why we don't see these machines much anymore, although I have read they are still around.