My read on the climate threat is more civilizational than extinctional, small numbers of people can survive even the "global nuclear war over resources" endgame of climate change. It's still a pretty horrible endpoint because so many of the easily accessible resources you'd need to kickstart another high tech civilization are already exploited and inaccessible in deeper mines but I have doubts even the worst outcomes would be human extinction.

Wouldn't there be tons of resources in the civilizational remains? Landfill mining would be incredible at least for a while.

For some things but rust will really destroy a lot of the valuable metals like iron as it decays then scatters, a lot of how useful that will stay will depend on how long and deep the collapse is. One of the main things will be energy as so much of the surface coal and easily accessible oil have been exploited. The best bet is probably recovering and refurbishing electric motors to rig generators but there's a lot of infrastructure around turning that into reliable power that would also be tough to recover.

As we ravage the natural world, one of the thoughts that has been able to keep me from being truly depressed is the certainty that we won't extinct all life. As beautiful as our biodiverse world is, I believe it will be differently and beautifully biodiverse in a couple hundred thousand years if we mess it all up.