No, not 100% failure over 40 years. But it is impossible to say that it will be 0. In the history of the US since 1776 till 2014, there have been big events like the American Revolution itself, the Civil War, the two World Wars, the Great Depression, etc... Quite a few big events in 238 years. So, how can we say that there's 0% chance of anything big happening in the next 40 years, that won't affect us in a bad way?
I again will say that I am more worried about something happens to me personally, the main thing being health deterioration. Something bad already happened to me while I least expected it, and I recovered but have "nice" surgical scars to show for it. [-]Many[/-] Most of us will not be posting here in 40 years. Anybody cares to make a guess how many will be left? Definitely not 97%. I am not sure of the age composition of posters here, but I think much less than 50%, maybe even [-]25%[/-] 10%, will be left standing, er breathing, as quite a few will be alive but bedridden.
And Bernstein was just rounding off 1333 years to a nice number of 1200. When we talk about probability and randomness, a rough order of magnitude is sufficient to make a point.