Why does extinction matter? If we lose civilization now, we'll be stuck at pre-industrial levels possibly for geological timescales, as we've mined and burned all the high-density energy sources you can get at without already being a high-tech industrial society.

I don't think that would necessarily limit us. Windmills and water mills can be made with wood, stone, and the small quantities of iron that pre-industrial societies could produce.

Sure, but it's hard to move from that to industrial production without having a high-density energy source (like coal) available.

Entropy