Re: How?
All ofthem I expect. There's no reason for an airport to need power backup for all its systems, and they rely on a lot of third party and off site services to work as well. For example air traffic control and coordination, parking, road networks, communications etc.
As a regional outage will affect all of that there's no cost-benefit to keeping anything other than emergency lighting and evacuation, and critical systems, operational as people won't be able to get to the airport, get away from the airport, or fly anywhere anyway.