The 12V battery is totally dead. If the tow truck driver is still there now, have the driver disconnect the 12V battery negative cable at the battery. Apply the jump cables to the positive cable and body ground, then see if the Prius will become READY and can be driven. If it can, then arrange for another tow truck to come tomorrow morning and repeat that process. Immediately drive the car to the local Toyota dealer or wherever you plan to purchase a replacement 12V battery. Obviously, once you make the car IG-OFF, it will remain that way until the car is jumped again or until a new 12V battery is installed.
The tow truck driver left before I read your suggestions. I’m planning to have it towed to the dealer in the morning.
You don't really have to tow to a dealer, just buy a new battery and install it. Make sure all your connections are tight. A dealer will do all that and charge you $350