I don't fear for civilisation in the slightest. Knowledge builds on knowledge to stay current. I don't need the original design documentation for the first ever wheel to know how how to make a modern one. We have lost countless things over the eons. We're not sure how the pyramids are built, we don't have design documents for the first aqueducts, we just know they existed but are unsure of how they figured out how to make them, we didn't know the Roman formulation for cement.
Yes civilization here has surpassed those losses of knowledge in every way. We've built bigger buildings than ever before, we've advanced sanitisation and water management in ways the Romans couldn't imagine. Even now we're using advanced computers with modern Unix kernels without any knowledge of what the source code to Unix V4 looks like. This is an archeological curiosity but not something that underpins our civilization in any way.
By the time we lose collective knowledge we've typically already surpassed needing it.