To be clear, under no circumstances is Kestrel's licence valid, and he should not fly based on it. The cardboard airmans cert are no longer valid. Only the credit card ones are now valid.
How he gets a new credit card one will depend on which sort of an FAA airmans cert he has.
Did he do the FAA Skills Test, and get a stand alone licence, or did he get one based on an ICAO licence?