I doubt anything can stop a Massive comet. Shooting up missiles at it probably works in movies not irl lol.
Unless your talking about 1-200 years from now, then we might have figured some shit out.
Well that all depend what material the comet or meteor is made of, soft hard ultra hard.
Right now a comet or meteor seems to be the only thing that could have a catastrophic civilization ending potential.
So if we can indenitfy each and every rock out there big enough to end our civilization you would be able to guide these
rocks out of our path, we have already landed probes on asteroids so it is possible.
The problem right now is that nobody wants to spend money on it meaning nobody seems to see any immediate danger which means
that most likely you will wake up at night one day and the next second your gone.