Well, we have vast piles of resources sitting around in landfills ;)
When the Roman Empire collapsed, and the Saxons saw the concrete aqueducts they left behind, they thought that a race of Giants had built them. They'd lost the ability to even comprehend what was involved in building such things any more. It took us about 1000 years to get back to that kind of constructional know-how.
But the Saxons thrived meanwhile. It turns out that you don't actually need concrete aqueducts in order to make babies.
I've wandered around SE Asia a bit. If Civilisation collapsed there's plenty of people there that wouldn't hear about it for a few years, and wouldn't care much even then. Life will go on. People will cope. They'll carry on having babies and growing food.
If we can just somehow make sure the knowledge survives, it might not even matter that much. Our descendants can work out other ways of building stuff, more suitable to the circumstances they find themselves in. Who knows? They may develop better solutions because they never had the easily strip-mined resources.
Japan had very poor iron ores. To make steel weapons they had to develop some incredible methods of forging this poor ore. They ended up producing (arguably) the best swords in the world. Constraints can be overcome and adapted to. We will cope.