The events in the book "Life as We Knew It"...are they possible?

Well, if an asteroid hit, it would create a tide wave of dust that would travel round the world destroying pretty much everything especially if it knocks us out of orbit which is unlikely. If the President had known about it before it happened, he would mostly try to save the scientists needed to kick-start the human race again. He would only save a few people not the millions in old nuclear underground bunkers.. Those who survived would die off eventually as we would need fuel, light and food to survive for a long term.