Recovery would be much faster than you think
Find a pre-1986 car, drive down to the computer museum. Start up the Altair, Imsai or Digital Group box, and start it normally: toggle in a bootstrap loader.
Toggle in means setting a memory address on the 16 address switches, then setting a data value on the 8 data switches, and hitting "WRITE", then autostepping to the next memory location, rinse wash repeat.
A bootstrap loader is an extremely short, ~100 byte program that can input data from some other I/O device, like a paper tape reader.
Use the paper tape reader to input your program, or hey - here's an idea, how about an operating system. You know, like Apple Monitor (2048 bytes) which included a lot of code to emulate a TTY on Apple's internal display and keyboard, not necessary, just use a physical TTY or VT100.
And now we break for lunch.
A few hundred bytes in the OS teaches it to read/write a cassette tape. Another couple thousand teach it to read/write disk drives. I'm not speculating, this is how they worked.
Meanwhile, parallel efforts are running on
storing the bootstrap loader in ROM somehow, to cut down on finger callouses
a primordial disk filesystem
a simple text editor (hmm, do VT100s still work?)
an assembler (assembly language compiler so we can say
LDA #INPUT_MODE instead of
And we better get dinner before all the restaurants close.
At this point we're doing command-line just as we do now, except using an actual VT100 instead of a Terminal/PuTTY window. We won't have an
ls -R because we don't have a recursive filesystem yet, but small steps Ellie.
Speaking of small steps, we start writing high level languages and cross-developing; i.e. use the Imsai to cross-compile 80386 to get the Compaq 386 booted up, (mind you, your very first x86 code would be native 32-bit and have no concept of the old 64k/1MB RAM barriers), then use that to cross-compile for the PowerMac G3, etc.
The hard part is coordination
The problem is, this effort is happening independently in every single location where a functioning Altair/Imsai/Digital Group machine exists. Now the challenge is coordinating the efforts when the phones are down. If the phones worked, any museum-piece 300 baud modem would get the crews talking and sharing code.
And the phone company is not idle; they're trying to figure out how to get something up.
About a day after telecomm is up, someone will have (re)written BBS software, assuming they didn't find an old copy of BBS source code in BYTE magazine. Now we're doing the same thing we do right here. This increases the speed of the rebuild ballistically - especially since every nation in the world has identified it as a national strategic priority.
Firmware is an annoyance
Unfortunately many components nowadays, like USB fobs, have "firmware" running on a lower level of the system, and don't really have a "hard" backdoor like the Imsai front-panel to force-load a bootstrap loader. If that firmware is gone, each machine would have to be hacked or scrapped. However that won't be a problem until we get into 2000's hardware, so that Pentium and Mac Quadra 800 will probably still run fine. And with those we can redesign/replace the other.
It's true that a Quadra 800 doesn't have a front panel of switches. It does, however, have traces on its PCB, and you would have to do some hardware hacking to get a bootstrap loader into it, or just learn to burn EPROMs.
We know the destination
Since the design problems are extremely well-defined and well-understood -- all that remains is code-slinging. We don't need to reinvent the wheel, we all know what wheels look like, we only need to carve one.
Remember, almost all existing code is understood by somebody who is alive, and who if pressed could rewrite it. Better.
It would be the best thing ever.
It would let us (heh) "reboot" our computing systems design from scratch, rather than constantly drag along old legacy infrastructure that makes everything complicated. Code would be streamlined and unified partly because we have to get the world back up, and there isn't time to support a bunch of legacy ways to do that same thing. DOSbox gone. Windows gone. Flash gone. HTML/CSS/AJAX morass streamlined. Etc. etc. The government would stomp all the patent issues owing to the national emergency.
Haven't you ever wished you could just take a month and scratch-rewrite all your legacy spaghetti code and obsolete standards? Now you can.