I think the most we can say is that there hasn't been a disaster in our history that would have required great luck to stop. Our world has nothing like the dust; our destruction is not nearly that intrinsically assured. So whatever coincidence saved us, anthropomorphically, would not look like an Act of Great Luck; it would look like the sort of thing that you could convince yourself in retrospect must have been more probable than it seemed at the time. Long, drawn-out sequences of individually credible chances.