Comment by mandevil

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.