More than 2 million research papers have disappeared from the Internet

Yes and to add to @rkaplan 's point I wonder how much of any importance is actually lost, some estimates say scientific papers alone are doubling every 9 years and have been for a long time. Hard to say too what are ‘quality’ papers, predatory publishing is a problem and for many of those it would be preferable that they were lost.
PubMed alone adds a million papers a year. Why PubMed is always the bench mark though… ’
I spoke once to someone at the British Library who said one of the problems he had aniticipated was not storing but having things to actually read some formats. I suppose those horrid micro-fiche newspaper files were an example?
I don’t know how that worked for peer review papers though.