Whenever I want to be depressed about the loss of human knowledge, I think about how no one will know how to build a VCR, or all the "hacks" and things that were needed to get it working. I'm sure they'll understand the concepts very well. It will be "simple" physics because it was discovered first (Like how a HDD uses earlier physics than a SSD).

But then I think of all the amazing people (that are on youtube) who restore old technology, and build replicas, etc, and I feel okay again about human knowledge.

But I think it is possible that as time goes on, knowledge about these systems can get lost, even if they're simpler to understand.