Humanity has already survived several impacts from smaller hits worldwide in the last few million years of mankinds existance, the last one being in a russian forest in the early 1900's. Today however and the greater population of the globe, any hit of any size would be catastrophic with an enormous loss of human life. The only sensible thing to do is have stellar rockets in orbit then use them to "push" away NEO after docking on to them. The evidence on this planet is clear on every continent ......and thats without the benefit of having visual impact evidence from the sea bed...but it would suggest from current evidence that we receive a "reasonable" hit every couple of hundred years.