It does not work that way. What you don't understand is the energy density multiplied by massive availability is what made the difference. There is chemistry in all of that too. We make so damn many things with fossil fuels it's hard to comprehend.

If we were to collapse, we would be left with some remnants that we would be unable to reproduce!

The tech needed for that runs on fuels we would find ourselves unable to procure.

That's coping, not building or bootstrapping.