I'd imagine people would block cars without passengers from escaping. Rip out the tracker and any other remote control components. Then tow it to a chop shop and sell the parts for scrap.
I guess network security will matter too. A thief could reroute a moving vehicle in transit and send it to their favourite chop-shop. In fact, given that you will only ever be a passenger in a self drive vehicle, why limit yourself to stealing empty cars?