If you are designated as the responsible driver on your rental contract, and you willfully or intentionally fail to return your rental vehicle on time to the owner or rental company, you may be held responsible for stealing the rental car. Of course, there may be other circumstances where you rented the vehicle but may not be held responsible if the car is later stolen.
For example, another authorized driver on the rental contract may flee with the vehicle. Or you may ask someone else to return the vehicle, but they fail to do so. Or you may have the vehicle criminally stolen from you by someone else. In those cases, you would likely be found to lack the criminal intent to deprive the rental car owner of the vehicle and would likely not be convicted for vehicle embezzlement.