It depends on the policy as to whether or not unlisted drivers are covered.

They should have checked their policy before tossing the keys to an unlisted driver.

Some insurance companies will refuse to cover an accident if the driver of the car isn't on their list. It depends on the policy you purchase.

>What else should drivers without a car or car insurance consider?
If you're a licensed driver who doesn't own a vehicle, you likely don't have a need for a long-term car insurance policy. But, what should you do if you need to temporarily borrow someone else's car? Here are some points to keep in mind:
The car owner's insurance policy may help provide coverage if you get into an accident.
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You may be responsible for certain types of damage, depending on the coverages the owner's car insurance policy includes. For instance, if their policy doesn't include collision coverage, you may have to pay for the repairs to their car if you cause an accident.

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>You may be responsible for costs that exceed the coverage limits on the owner's car insurance policy.

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>If you're planning to lend your car to a friend or family member, or borrow one from someone else, remember that it's a good idea to review both of your insurance policies first. Your insurance provider can also help answer any questions about your policy before you decide whether lending your car makes sense for you.

Source.

His finding a way to pay it.

Otherwise, it's going to hit his mother and grandmother, because their names are listed on the policy.