Hi Mr. R.:
I worked in a bike shop for five years up until two years ago and my better half continues to work in a bike shop to this day.
I have to say having a road (or “racing”) bike for when the SHTF is a really bad idea. Road bikes are kind of like the sports cars of the bicycling world. They are not meant to beat upon, you run over or hit the wrong thing on the road or whatever–even gravel–and you could be walking. They eat tires and tubes. I have changed hundreds, maybe a thousand or two road bike tubes, usually because of a small piece of steel belt from a car tire, or thorns, were embedded in the tire. Kevlar liners help a little. Also, most road bike tires run between 80 to 130 PSI. Pumping them to that pressure can be a chore for the weak or small statured person [, especially when using a small clip-on touring pump].
The most replaced parts on a bike are going to be the tubes, then the tires. From there parts breakage begins to vary widely, I would say the best bike for when the SHTF would have to be a hard tail mountain bike. Skip the road bikes and comfort bikes. In essence: You can ride a Mountain bike anywhere a road bike or comfort bike can go, but not vise versa. Also, as much as I love downhill and free ride bicycles , stay away from these beasts for SHTF, since you most likely will not break one, and if you do you will be broken too (trust me). They are on the opposite end of the spectrum from a road bike. Full suspension is awesome,I love mine, but if I were in a grid down mess, and toasted a pivot bearing, I would then be SOL. There can be lots of pivots and bearings, air shocks, although much much better now than the past can be a a problem.
Bike shop brands are going to be the best bet, but not essential. Up until left the industry a couple of years ago, the majority of big name frames were made by Giant, and then Fuji. So as far as weld quality, they are going to be close. Also, as awesome as Carbon frames and parts are, stay away from them, that carbon framed bike is super strong with riding forces, but lay that bad boy down and pinch the top tube or down tube and you bay get a really big surprise that could cost you a grand or two, and in the SHTF, it will be a total loss (unless you have vacuum bags and a high heat high pressure autoclave.) Also carbon fiber frames can fail in quite a dramatic fashion, leaving little shards of carbon in you to pick out.
You really do get what you pay for up to a point as far as strength and quality. There is a point you start paying for weight and technology, and that means next to nothing in a grid down situation. I can expand on this in great detail if you would like, this is just the tip of the iceberg, i really do think that in a SHTF situation, bicycles will be essential. – J., Esse Quam Videri