What we need to do is put more money into tracking Near Earth Objects (NEOs), especially in the southern hemisphere where there are far fewer amateur astronomers tracking these things. It would not have to be hugely expensive. Just getting the appropriate small telescopes out to interested science/education groups in a coordinated sky surveying program. Then if something big is getting too close, we might have enough advance notice to actually do something useful about it.
Put such a program under the auspices of the UN. Then we will have enough notice and still not do anything useful to avert the catastrophe. (/gratuitous swipe at UN).