We don't need mining - The metal in junk yards and recycling centres are a lot easier to access than building a mine in the middle of nowhere going underground 50 to 100 metres. The only reason we do mine and need new metal is because metal from junkyards and recycling centres are needed as well, and all existing metal is already being used. If most humans die off then the existing metal are available for reuse. And it's as easy as heating it up past melting point and molding it into the right shape; There might be ways to do that optimally but in the case where plentiful resources are available compared to human capital, it should suffice.

The oil is gone, but coal is still easy to access. We can bootstrap off a second coal industrial revolution. And every person who've been through high school knows the principles involved in generating power from coal, though might be lacking in the actual techniques.

> but only to sell, not to use

You've proved there's buyers who would find a use for it.