It's perfectly safe to tow the car with the drivetrain freewheeling. After all, it's no different to driving the car 200 miles. This only applies to cars with manual transmissions though; you can cause damage to an automatic transmission if you let the drivetrain freewheel. This is because the hydraulic pump is on the input shaft of the auto, which means there is no oil pressure if the engine isn't running. No oil pressure = no lubrication = dead auto.