His insurance company should cover the loss, and a local lawyer can help hold the insurance company's feet to the fire, as rental companies are notorious for scamming people with inflated losses.
insurance companies and credit card companies are notorious for minimizing payments. Get an attorney to protect your rights.
The author of this answer is an Attorney-at-Law, licensed to practice law only in the state of Arizona. Unless both you and the author have signed a formal retainer agreement, you are not the author's client, and the author's discussion of issues does not constitute legal advice. Opinions expressed herein are solely those of the author, and are neither privileged nor confidential.
His insurance should pay just as if he wrecked his own car. So, the deductible will be his to pay. Unless the rental contract also says he has to pay for diminished value, that should cover it.
This is a summary based on incomplete facts. You should not rely on it as legal advise. No attorney-client relationship is intended to be formed.
This question is difficult to fully answer without being able to review all of the contracts involved. However, a local attorney can do this for you to help protect your rights and make sure that the insurance companies properly value everything.
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