Cooling System Failure, What to do?

If your cooling system fails and your engine starts to overheat, the only “system” in-place to protect your engine from destruction are dashboard warning lights and (if your car has one) the temperature gauge. Almost every engine that I know of will keep running after overheating until permanent damage occurs. This is because manufacturers assume that it could be hazardous to shut down the engine while you are driving.
There are some exceptions. Many turbocharged engines will reduce the maximum allowable boost when you are near overheating temperatures, and some engines with cylinder deactivaton systems will default into the the low-power mode to help protect the engine. IF you have a big cooling system failure, like broken water pump drive, loss of coolant, or total blockage of the radiator, you will still overheat.
You might say that the ultimate protection against engine damage with coolant system failure is the large amount of steam and hot coolant that will get sprayed all over the front of the engine compartment when the cooling system finally boils-over. You really have to pull-over and turn of the engine when that happens!