Try moving the pages from the problem file into a new file using the Move Pages command in the Pages panel menu. If you can then export that one to .idml you can replace the file in the book.
Unfortunately, indesign crashes when trying to move the pages too.
Are there any other options?
Copy/Paste In Place to a new file spread by spread...
I have had a similar problem
1. couldn't save to IDML - CS6 crashed as soon as I tried to do anything
2. Opened the file in CC - it crashed there as well as soon as I changed anything
3 deleted my preferences, uninstalled and reinstalled the font - no change
4. copying or moving pages didn't work - too cumbersome as I could only perform 1 action b4 crashing the bad fiel
Like you - I had been working in the ToC - minor changes to the formatting - when it crashed
I was able to create a new clean file - importing all the styles, masters from the bad file then was able to in bad file - open the text editor [ctrl-y] and export as tagged text.
Successfully imported this file into the new clean file and voila - most everything was there - still had o t make some minor modifications - but most of my work was intact!