Come on now. The Gamalons were lobbing big, high speed asteroids at us and we only needed to worry about the radiation. But the Earth will survive!
Actually, radiation is about the only thing you don't have to worry about... I recollect that, at the time of the Halle comet encounter one of my colleagues was of the opinion that if it impacted it would produce an enormous crater and demolish a few square miles. and I thought that was a bit of an underestimate. When we did the maths it turned out that the resultant kinetic energy was the equivalent of giving every man woman and child on the planet a small atomic bomb and asking them to explode them simultaneously.... (of course, comets are 10s of km in size and fall in from athe edges of the solar system so can have closing velocities of up to 60km/sec).
And you wouidn't have to worry about global warming either - the resultant fimbulwinter would take care of that for decades....
