Under many circumstances repayment of PIP is waived in Washington. If you doubt your attorney ask to see the waiver letter. In other cases PIP may not be waived however, where you have received all or substantially all of the third partie's insurance the "made whole" rule recognized in Washington will allow you to avoid subrogated interests that are subject to state law.
Yes. If your son did not do the damage intentionally your homeowner's insurance will probably cover this, call your agent and ask. If the car owner turns it over to his auto insurance you may find them chasing you to recover their payments to repair the car. The bottom line is that you may want to pay this yourself to keep your insurance out of it.