depends on what type of bike your riding. belt drive, you'll roll to a stop, quickly. chain drive you might skid. it's like slamming on your back brake, but it really depends on whether the clutch lets go or not. if you seize on a pit of sand or an oil slick, maybe you'll lose control. I suppose you could get tossed if your kinda drunkers too.
rider being thrown is usually more of a front wheel/brake problem or loss of control. I'm far more afraid of the idea of front wheel seizing than engine seizing.