You have about as much chance of that happening on a trainer. If you happen to turn the wheel and slide off the rollers you will move maybe 1-2 feet. Since you are all of a sudden hitting the ground and tries to force you to go forward and you have no momentum so stop pretty quickly. At first it does take a bit of practice but after 2-3 times you have it down pretty good.
A few manufactures do not warranty their frames when used on trainer, so you might want to check into that.