destroying HAILLEYS doesn't stop planet's progression

Now what if the halleys guide the asteroid to a trajectory that heads straight towards the target planet. But the timing of when the asteroid starts his engines is just right so that when the halley hits, the target point was facing directly towards the incoming asteroid.
Meaning that in the initial calculations, the rotational speed of the target planet is calculated for in a way that the target area will be accessible without the use of engines.
(Collision plane wouldn't be perpendicular with the line between the center of the 2 bodies, but that's not important)

Anyway, this was just to prove there is a way to achieve this. I think this wouldn't be the best idea/solution gameplay wise.