I agree there are much better examples. I think Historically more significant loses have happened. There is trove of techniques Gauss solved 100 years in advance that were not communicated and lost. Example here being FFTs which were not rediscovered until post ww2.

I think the question is also really hard to answer in a non-answerable way because if you don't know you've forgotten who do something you simply just don't know. If you sub-divide humanity in to factions certain factions have lost the economic ability of doing some things for example have been lost to America. While humanity can still do it certain places would be totally lost without the existing tribal knowledge. It would take us a long time to reinvigorate a tool and die industry in America its not a lost thing but if you can't do it commercial currently can you do it at all?

Hopefully that's nota weird direction to take the discussion in