I gotta do a re-watch. I wasn't sure of the Vengeance was already going to crash like the Enterprise.
Both ships were in bad shape, the Vengeance could have been pulled in by gravity.
And yeah, I'm sure Khan wanted to crash into Command at that point.
I think the Vengeance could maneuver and Khan wanted to collide with the Enterprise but because of the dodgy engines he missed and so he decided to destroy Starfleet instead.