Suppose you're flying a big plane in to an airport like Mexico City, already in final descent, when an earthquake strikes. Large cracks appear in the paved infrastructure catching some vehicles by surprise. The airport suspends operations. Planes planning to take off are stuck on the tarmac for at least several hours. Planes planning to come in from farther away are told not to, maybe from an external seismic monitoring service if communications are out. Those already in the air but far enough away to be able to divert can land at other airports.
Yesterday, the main infrastructure was inspected and found to be OK, and the airport reopened several hours later. But what would have happened if the earthquake had been strong enough to destroy the runway or other landing-critical infrastructure at this airport and at the nearest alternative, so that neither "rack & stack holding patterns" nor "just go to the alternate" (as in e.g. a terrorist takeover at one airport) are viable options? Are there special rules/considerations in place to help protect safety in such a rare region-affecting event?
Continuing the distinguishing analogy from the terrorist takeover question, this situation is more like a widespread cyber-attack, solar flare, or electromagnetic pulse that knocks out ground facilities and prevents landing at multiple airports without destroying in-air flights in a way that e.g. a sudden volcanic eruption or nuclear explosion might. This question also focuses on emergencies that arise quickly and without the kind of notice that would permit a planned closure (as e.g. a hurricane would).