Under the FAA's slot allocation guidelines, a carrier must generally use a slot 80% of the available time or it can be reclaimed by the FAA. That said, carriers can lease their slots to other airlines so theoretically, AA could reduce its flights at JFK and lease the freed up slots to another airline (perhaps another OW member). It sure looks like AA is intent on paring back domestic service at JFK to just hub routes, west coast premium and a few key routes while relying on LGA for short/mid domestic hops and the bet is that this will be enough to keep corporate accounts happy.
From the FAA's order on JFK slots:
7. For the duration of this Order, a carrier may enter into a lease or trade of an Operating Authorization to another carrier for any consideration. Notice of a trade or lease under this paragraph must be submitted in writing to the FAA Slot Administration Office and must come from a designated representative of each carrier. The FAA must confirm and approve these transactions in writing prior to the effective date of the transaction. The FAA will approve transfers between carriers under the same marketing control up to five business days after the actual operation, but only to accommodate operational disruptions that occur on the same day of the scheduled operation. The FAA's approval of a trade or lease does not constitute a commitment by the FAA to grant the associated historical rights to any operator in the event that slot controls continue at JFK after this order expires.
8. A carrier may not buy, sell, trade, or transfer an Operating Authorization, except as described in paragraph 7.