Pole flip is in no way comparable to a giant killer asteroid impact. We all might get more cancer more often for two or three generations. Bad, yes,.but hardly civilization-endangering. Giant killer asteroids tend to create widespread destruction through the impact itself, a likely-to-happen global tsunami, kicking so much dust into the atmosphere as to ruin harvests for up to a decade, trigger dormant volvanos (such as the Yellowstone magma chamber), whose break-outs could then emit so much toxic gases that it flips the acidicy of the oceans, disrupting the maritime food chains as well. Insofar, a much, much deeper and more widespread damage to countless ecosystems with the disruption of food supply, and more or less immediate extinction of multiple species.
Just because two disasters are "bad" doesn't mean that they are bad on the same scale. There's bad, worse, terrible, and then there "killer asteroid bad". Beyond that, "nearby supernova", "targeted gamma ray burst", drifting cold neutron star from outer space, then nearby merger of two massive black holes. A pole flip is somewhere between "bad" and "worse", and anything above "murder asteroid" is irrelevant for mankind in its current development stage because it'd be end times, anyway.