There are something like 20,000 airports and heliports across the US. While not all of them can handle 747s probably there are several thousand fields that can take one of them, especially if there is no need for it to fly again.

And even if all of those fields are destroyed in the US, the 747s modified for AF1 (VC-25s) are capable of in flight refueling, they can stay up for about three days before the oil needs to be changed on the engines and they are forced to land. So they can still reach Australia or some place far away from the US if the rest of the US is totally destroyed.

Given the extent of planning that went into these types of doomsday survival scenarios, I wouldn't be surprised to find there are pre-prepared discreet runways in obscure locations unlikely to be targeted. Not full concrete runways, just a strip of prepared land that would see a 747 land without exploding into a ball of fire.

Dry lake beds abound in the US West. See Edwards AFB (big dry lake bed on which nearly everything, including the Space Shuttle, has landed). See also Groom Lake. These are enormous and couldn't be wrecked by conventional runway denial weapons.

Those interstate highways are starting to look pretty good as the fuel guage drops

I'd always been told this was planned into the implementation of the US Interstate Highway System. There are dead straight and level sections ever so many linear miles or per some gridsquare measure to serve as ad hoc landing strips in a national crisis. That's been 35+ years ago that I heard it and I haven't sought any supporting documentation since the dawn of the Internet. Any insight would be appreciated.

even a small country like Switzerland uses its highways to land fighterjets[0], wouldn't be weird to me if the US with their humongous highways uses them for the same reason. difference is that the swiss have to remove the middle crash barriers before landing, so less spontaneous.

[0]https://www.swissinfo.ch/eng/swiss-air-force-lands-fighter-p...