Dissappear? No, of course not

Fall out of repair, and be unable to be repaired effectively without tools, resources, or knowledge that are no longer accessible?

Abso-fucking-lutely

Take a deep sea oil rig. How long do you think it’ll be operational without maintenance with all that sea water? After not too long you won’t be able to repair the damage without serious industrial capabilities, and that’s assuming you even know how to fix it.

Really even as relatively little as a few decades of total chaos and disorganization would be enough to make crawling back really hard. A century and more and it really could be impossible, or at least improbable - especially given that the humanity that comes out of the other end of the crisis is the same one that got us into it. So the remaining pieces of major valuable infrastructure left will probably get wrecked as the survivors fight over them

True, but Its 100% possible for us to get knocked back into the iron age, and if that happens, there’s a very real chance we won’t be able to climb up again.

Easy to access sources of a lot of the resources needed to rebuild a modern civilization are gone, the only reason we can get to the remaining deposits is because we already have the advanced equipment to extract it. It’s entirely possible that if we get knocked back down the tech ladder, we may never climb back up again