As crazy as dinosaurs worrying about asteroid deflection... oh, wait
Seriously, I'm with ER. Worrying about how to save ourselves from a catastrophe in the year 5,000,002,008 AD using physics/engineering we can forecast today seems more than a little premature. Several orders of magnitude more premature than Neaderthals trying to figure out how to reach the Moon using only boulders and antelope bones. You can imagine some amusing bull sessions around the campfire discussing it, but I wouldn't bet on them having come up with a practical lunar lander....