I don't think this is necessarily a bad thing. For one, the 80/20 rule applied back then just as it does today, so most of what's lost is crap to begin with. It's no different than in the real world: surely nobody's lamenting that you can't pick up a copy of Fordyce's Sermons anymore (and I presume that it'd be long forgotten if not for Austen). While some valuable resources were undoubtedly lost, most live on re-posted elsewhere, like memes, but in a "good" way.
Secondly, the book is more analogous to a map or dictionary, and it ought to be a descriptive source, not a prescriptive one. Some language purists may disagree, but I could care less :-). And similar to an old, outdated, map, you'd expect that the details may have changed, but the landmarks are most likely still accurate. NASA's still nasa.gov, MIT's still mit.edu -- well, IIRC www.mit.edu used to point to their library's portal, and web.mit.edu their main page; I see that's changed -- and CompuServ still...exists.
Secondly, the book is more analogous to a map or dictionary, and it ought to be a descriptive source, not a prescriptive one. Some language purists may disagree, but I could care less :-). And similar to an old, outdated, map, you'd expect that the details may have changed, but the landmarks are most likely still accurate. NASA's still nasa.gov, MIT's still mit.edu -- well, IIRC www.mit.edu used to point to their library's portal, and web.mit.edu their main page; I see that's changed -- and CompuServ still...exists.