In most cases, the unauthorized driver will be liable for the damage to the rental car, as well as any other associated costs, such as towing and storage fees. The rental company may also have the right to pursue legal action against the unauthorized driver to recover the costs of the damage.
It is important to note that the terms and conditions of the rental agreement may vary from company to company, so it is important to carefully read and understand the agreement before signing it. The rental agreement will typically outline the responsibilities of the renter and any additional drivers, as well as the consequences for unauthorized use of the rental car.