Masterplan
Bob,
"Is there some kind of diversion master plan should Heathrow become closed?"
In theory we never close. Even with the fire alarm in the new tower, ops were only suspended a short while whilst evac procedures were completed and emergency tower up and running. If we have an incident it will invariably only involve one runway (BAW38). We would then run the available runway as single runway like any other UK airfield. Heavy flow rates would apply and short haul traffic bear the brunt of delays (long haul inbound would already be airborne and on its way). Problem here is that any flow rates applied will take a minimum of one hour to have any effect on traffic arriving at the stacks, anticipate an hour plus of a very busy TMA.
With regard to diversions we would attempt to give accurate EAT's asap (whilst the situation is fluid, EAT's can be a little flexible). It would be up to the aircraft concerned to inform ATC as to their ability to meet EAT's or the need for diversion. In a major dispersal of traffic the supervisors would be talking to other airfields, Gatwick etc to understand how many diversions they can accept (i.e. only so many wide body stands are available etc). Although in extreme scenarios, taxiways would be used to park aircraft and long delays on the ground waiting for ground handling.
Brief overview, hope it helps some
2.5