You say that your friend has already bought the aircraft.....are you sure that the aircraft is still registered? Normal practice is for the seller to deliver a bill of sale to the FAA and the FAA will act on that. If the buyer is a non-US qualifier then the aircraft is deregistered. Getting it back on the register will require the action of somebody properly qualified. And a little money, of course.
Don't ever crystallise a deal without knowing your course of action. A stateless aircraft cannot be flown at all!