FR have to hand the slots back to IAG ,so unless someone else wants to pick up the BHD/LGW route and use these slots ,I don't think there is anything to stop either EI or BA reintroducing the service with these slots ( regardless of the OM slots ).
Think IAG are concentrating on yield improvement on BHD/LHR ( hence frequency reduction this winter) , so they probably don't want to add London capacity elsewhere unless they think it's totally different market.