Wonder what they'll think if the impactor just goes right through the comet?
That's not possible. Though they don't know a lot about the comet, they have a rough idea of it's mass and a rougher idea of it's density due to it's orbital motions. The density of comets like this is just a little bit higher than that of frozen water, which is why they call them "dirty snowballs". At any rate, there WILL be an impact, that is for certain.
I was just thinking the same thought. I was also thinking that space-base impactors should be a military weapon. Space is the ultimate high ground and I would love to see jihadists blown up from tungsten rods shot down from the heavens.