I guess they'd be reincarnated as cockroaches. Aren't they supposed to be able to survive stuff like this?

On the other hand, we could divert the asteroid (whether the world's governments would get their acts together and do so is another matter), but suppose the asteroid then slammed into a faraway planet where the inhabitants lived the pastoral life of global peace that we crave, and had no means of destroying the asteroid before it hit them because they'd never invented warheads or military satellites or the like? (Whaddaya mean, "Tough sh**"? *G*)