Looks like your concerns are 2 separate issues: liability coverage and collision damage coverage.

Unlike most states, California does not require rental agencies to include the minimum liability insurance required by law for rentals. However, Hertz's website states that: "Hertz provides no liability protection under the terms of the Rental Agreement to the renter from claims of injury by others against you resulting from an accident. Your personal/business insurance may cover your liability. Exceptions: Hertz will provide primary liability protection up to the statutory minimum limits to international customers (driver's license indicates an address outside the USA) renting in California."

Therefore, it looks like your rental should've been covered by the state's minimum liability insurance even if you didn't book on an international site as you presumably had a foreign licence as per the Hertz terms. While woefully inadequate, it should be fine as you said there were no injuries to the other party. The minimum insurance coverage keeps you kosher with regards to driving lawfully as you only need liability insurance when driving, collision/comprehensive is optional. IANAL, but the liability insurance could even cover the deductible or repairs for the other vehicle.

If you're sure that you do not have collision damage coverage from a credit card or personal insurance, then you will be responsible for the repairs and loss of use for the Hertz vehicle. Be sure to ask for a summary of repair and loss of use charges.