If your traction battery (HV) discharges too far, you have the car towed to a Toyota dealer.

The TCH does not have a 12V starter or alternator. The HSD (hybrid synergy drive) uses the HV battery to start the ICE, and recharges the HV battery. Once the TCH powers up the HSD, a 12V inverter provides up to 1KW of 12V power and recharges the 12V battery. The purpose of the 12V battery is to provide enough power to start up the computers, and power 12V accessories when the HSD is off. Only about 10 amps is needed to "jump" the 12V battery so the TCH computers power up.

I remember reading that if the TCH sits for two months, you are supposed to start the car and let it idle for at least 30 minutes to recharge the batteries. The dealer has special equipment to charge the 240V HV battery, should it be necessary. Oddly Ford's FEH has an emergency start proceedure that will "boost" the HV battery from the 12V battery so you can attempt to start the ICE if the HV battery SOC is too low. It does surprise me that Toyota doesn't have something similar.

If your 12V battery dies, jump it from another vehical and be on your way. Be aware the 12V battery is a AGM battery, and should only be charged at 2 amps. If you use a 10amp charger, you can easily overcharge the battery and shorten it's life.