You make an excellent point. Maybe Thomas Midgley, Jr. was actually an alien bent on the destruction of Earth's galactic expansion potential. He was, after all, the person responsible for both leaded gas, and chlorofluorocarbons.

You can smelt aluminium with as little as a candle. Its normally incredibly hard to refine but we've left tons of that stuff in pure form all over the place. Fossil fuels would likely be a pain but charcoal exists and would do buffalo buffalo buffalo buffalo buffalo for smelting iron with a well built forge, It'd be harder to do but finding clearly artifical constructs made of the stuff would probably give them a huge incentive to figure out how to melt the stuff as opposed to our civilization that didn't even know iron could be smelted for a really long time.

You misinterpreted what I meant.

"Those who come after" doesn't mean someone's coming after us as in chasing us.

Those who come after as in those who exist after us. Future humans or whatever species takes over after we inevitably fuck ourselves over.

Edit: I'm the dumb dumbass here. I'm the one who misinterpreted what was said.

As a true rebuttal with my updated understanding, I don't see humans dying out. We already survived one mass extinction. I have no doubt we'll in one way or another survive the next.

Shanty towns might be the highest form of recycling we can manage.