A fallen off car exhaust could be dangerous as even though the catalytic converter provides extra safety and protection, the risk that carbon monoxide gets into the car is still dangerously high.
On the above car the customer even attempted to tie up the exhaust instead of taking it to a garage.
No need to elaborate on the health and safety hazards to yourself as well other road users and pedestrians, and that you would be stopped by the police. However, in this particular case had the customer gone to a garage straight away, all that would have been required was an exhaust rubber. As it happened though, due to the exhaust having been insecurely mounted to the car, a new exhaust was required altogether.
To ensure this doesn’t happen to you make sure you have your car regularly maintained. Prevention is better than cure. Always.