I'm all for the mental exercise of pure sustainability. It's how we should start all model making exercises. Fortunately, there's a huge range of possible paths to the future if we simply establish some (any) form of moderation of consumption as the primary tool of civilization. There's a big difference between the free market unfettered automobile-movement economy (that's really what we have: an economy based on moving cars around) and one based on people staying near their places to contribute useful labor to that place instead of extracting resources for the benefit of the cars (tanks, airplanes, warships, etc).

Did you know that Rudolf Diesel originally designed his engine to run on vegetable oil?

We need to consider the simple things that change our perspective of the purpose of human beings as contributors, rather than extractors and consumers.

Not that it matters. When it all collapses, many population-decimated generations can survive on readily available parts and materials that will be lying around.

Rebuilding the population and cities just won't be an option.

Whether the collapse happens tomorrow or in 50 years, it is inevitable for an unfettered extractive system.

The Amish are using electric bikes now. The end is near ;)