[oceanplexian]

We are now but if humans go back to the stone age because of a world war or something, we may not have a second chance. The people after us will have none of the same advantages since we extracted all the easily accessible fossil fuels that made the industrial revolution possible.

[roywiggins]

If you aren't worried about humans per se, a billion years is probably enough time to regenerate fossil fuels and evolve another technological species from scratch. Probably quite unlikely, but still. It's a very long time.