THIS is why I never throw anything away! Old computer to the rescue!
It's sad how slow my writing life has been over the last year, but it's also a really good thing, because I was able to recover pretty much everything in that corrupted Books file by retrieving the folder off my previous laptop. The only un-updated thing was my current MS, which I've been saving chapter by chapter on Google Documents and was also able to save through Word into the new folder.
So, as far as I can tell, disaster has been averted. Time for bed.