When SAAS have cases going, for extended times, they will organise what would be considered to fire service as COQ - Back fill those stations with other units (unless volunteer), or, they will recall crews - eg - regional fulltime stations.
In a scenario like you mentioned, they would clear cases or a lower cat. and divert, or indeed, respond nearest resource.
Metro response, a car would clear from a lower Cat case, in regional areas yes, sometimes waiting that long is how long it takes.. The chance one takes when they live out of metropolitis.
No, fire service would not get responded to a report of heart attack, they are not trained in the protocols to deal with it, the nearest Ambulance would get the call.