It's probably not a good model as that's an absolute giant as asteroids go. The one at the end of the Cretacous would have had 1/10000 or something of this one'

It's probably not a good model as that's an absolute giant as asteroids go. The one at the end of the Cretacous would have had 1/10000 or something of this one's mass, and we consider that a planet killer already. I think a 500km monster really is exceedingly unlikely, there are a lot less of those and getting hurled in our direction probably gets way harder, too, at that size. More realistic scenarios with smaller (city-scale) bolides would be absolutely devastating, too, but still way more survivable.