It should be nice to have these ai modes ingame. When ai will be set to "offroad" mode, vehicle will ignore waypoints. "Onroad" will be same as now.
But if you did that, the AI would crash a lot off-road. They would have to make the AI detect the angle of the ground and stuff to find the proper way to off-road. I just saw the AI drive a k series of a cliff because it didn't know it was there.
It will just ignore waypoints, so it will drive like there are no roads. Try chase or flee on the map like ghosts desert or gridmap.