The normal attendance of the 'outside fire service' (and other services - ambulance/police etc) at an Airport emergency, is surely essentially the same as any other call out. It is done based on availability and priority. If there was already a major incident in progress elsewhere, the response to an Airport call out might take longer, whilst crews are redeployed from other fire stations.
During the strikes, the military crews will endeavour to operate on a similar basis, albeit with considerably reduced resources. There is no escaping the reduced cover, whether you are travelling by plane/train/car or whatever.
It would seem that the legal requirement, during the strikes, for Airport emergency plans involving the outside safety services, still applies. My guess is that the regulatory authorities will 'deem' that the military cover enables Airport Authorities to comply with the terms of their licence.
