Unsure if you (the OP) means booking code F or a ticket in First Class. If the later and if a part of an AONEx fare, then expect nothing from the invol downgrade. Been there, complained, and nothing eventuated - but it was on a CX issued ticket, so AA may be a different outcome.
Indeed. if it is an ATW ticket such as a AONEx, the fare rules state
Code:
NOTE - FOR FLIGHTS WHERE FIRST OR BUSINESS CLASS
IS NOT OFFERED OR AVAILABLE PASSENGERS MAY TRAVEL
IN A LOWER CLASS IN THE APPLICABLE BOOKING CODE
FOR THAT LOWER CLASS. THE FARE FOR THE HIGHEST
CLASS USED APPLIES WITHOUT COMPENSATION.