Blast, I have to confess to not reading the book, and it's been years since I was in somewhat regular correspondence with FerFal but the gyst of what I got from discussions with him was your typical "modular replacement" type repairman that just pulls a part off a shelf and replaces it, a la changing hard drives, had a tough row to hoe, but a real repairman/craftsman capable of fabricating and modifying or repairing things would be able to get by. This is supported by my own experiences in third world countries as well as other areas of austerity.
Folks who can improvise, adapt and modify things in their environment to their needs tend to be successful survivors. Rigid thinkers do not.
I have seen some very ingenious repairs by "bubbas" or semiliterate peasants that have been actually very innovative. Those kind of folks will survive in the jungles of the Philippines, the hills of Arkansas or the streets of New York regardless of circumstances.