What DR said. If there's a capacity reduction it's down to the airline to comply-
Usually the airline then looks at cancelling flights to which there's more than one daily service, flights to destinations close at hand to the originating airport where pax might be able to get using alternative means of transport e.g. hire car/train etc..what they will probably try an avoid is wide body longhaul cancellations of perhaps the only daily flight to a particular destination.