Just to clarify, this is a vulnerability for cars with keyless entry. IE when you approach close enough to the car, it unlocks automatically if you have the key on your person, and you can start the car with the pushbutton without inserting a key. This attack makes the car consider "close enough" to be 100m instead of a few feet. If the key is inside your house a couple dozen meters away, the car unlocks automatically and you can drive it away.
Most smart key systems will let the car run indefinitely, or until it runs out of gas, etc, once the smart key is removed from range, provided you don't turn the car off.
This is done for obvious safety reasons. Imagine for example if a car just suddenly turned off while you were going over a major highway bridge with no shoulders, etc.
While I was driving a friends keyless car (he had the key) he stepped out to get something and the car flashed some lights to inform me I was driving without the key. It didn't turn off (thankfully). This is the correct behavior.
I once watched a friend's girlfriend throw his cell phone out of the car while on the freeway. Had this been his car keys I would hope that the car would not immediately power off (especially since I was in the car).
