You laugh, but we've actually had this happen before to a stock car. The rear most car on a 3 pack car carrier fell off the back and was only holding onto the tray by the front wheels. The car was chained to the one in front and the chain snapped when the driver went around a roundabout. To make things worse, he couldn't actually then get it off because of the angle it was on, all the fuel had run to the back of the tank and it wouldn't start (cars come to us with next to no fuel in them). So a few of us went out there with a jerry can of fuel and it was not lined up straight either, so we had to bounce it over (it was an Astra coupe) until it lined up with the ramps at the back. Luckily there was no damage to it.
We've had numerous cars damaged by train derailments, top deck trailers breaking and crushing the car under it. Years ago Ford even had a car carrier sink on the way to Australia! Imagine getting that phone call, 'sorry, the boat your car was on actually sunk'!