Your assumption is incorrect. It will run until the car is turned off. If it behaved as you're assuming it would be wildly unsafe, imagine someone inadvertently

Your assumption is incorrect. It will run until the car is turned off. If it behaved as you're assuming it would be wildly unsafe, imagine someone inadvertently dropping off a passenger who has the key with them in a purse or jacket pocket, then stopping briefly on a bridge without shoulders, or a railroad crossing.