Dooku wouldn't let Grievous get that far. If the Good General didn't play things Dooku's way, he'd fix Grievous. He'd have all the droids on his ship label him a target just like he did Asajj Ventress, and he'd be on the run. Yea he most likely would escape, but he wouldn't have anything to command. That's the thing about Droid Armies...they are not very loyal...except to the one controlling them with a master control.
He just can't catch a break.