It would be insane to ask a pilot to crash into a vehicle carrying a terror leader simply to take that leader out (such a vehicle would not be on a suicide mission. Terror leaders don't do that sort of thing themselves.) It would also assume a lot of weird circumstances, such as this pilot somehow being out of all communication, and unable to relay his position and situation via any number of redundant systems. How far could the car move before reinforcements showed up, or a Predator locked in?

The second scenario, a terrorist airplane heading for a city with no time to call in help, is totally different. I could see many brave pilots choosing to ram the plane rather than let it reach an innocent population. There are cases on record of pilots who have ridden their own crippled aircraft into the ground rather than eject and let it fall into a populated area.