Relatively speaking, there is very little data to go off of as of now. The comet hasn't been tracked long enough for them to truly see if it will even be close to Mars.

I do think, however, that if it does look well on its way to hitting Mars, it'd be worth while to send a large chunk of mass and try to push it in another direction. It could prove to be a trial for a future, Earth-threatening instance. So far the ability to deflect a comet/asteroid is only a theory--putting it to practice is a great way to test it.