I wonder if IR imaging can be used to read the books burned in 1944 by the German army at the Krasiński Library in Warsaw [1].
Many manuscripts among them were never reproduced. A random example: Jan Ostroróg's chess primer written between 1602 and 1610, where he supposedly invented the algebraic notation (a-h 1-8) over a hundred years before Philipp Stamma, to whom it is usually credited [2, in Polish].
That book looks way beyond repair tbh. But I imagine this technique could be used for others. The Nag Hammadi texts [1] come to mind as a potential candidate.
The danger of these things happening (could just be a regular fire) are why today every library with unique works should immediately copy them. Just take pictures of every page, put them on the internet.
Before today maybe you could take pictures. But they want to control them, or they have too many to get around to it. There's no excuse for not taking pics today.
http://gnosis.org/naghamm/nhlalpha.html
Edit: link with actual images of the collection - http://ccdl.libraries.claremont.edu/cdm/landingpage/collecti...