> maybe we can get it or some of the pieces to swerve into an earth orbit!
Not with a measly 800 pound kinetic impactor, you won't.
How fast will that measly 800 pound kinetic impactor be travelling when it hits the comet? The article doesn't say, but does state, "According to a senior official associated with the project, the impact, they hope, will put an end to all the speculation about the interiors of comets." That reference to the interior of the comet leads me to believe that it's planned to be a big enough collision to break apart at least parts of the comet. I would be very surprised to learn that they have calculated the trajectories of the pieces that break off.
Cordially,