If you're using Win7 (or Vista) you might be able to use the Previous Versions feature
Open the book path, right click the epub file, select Properties, if the feature is configured you'll see a Tab called Previous Versions, open it and wait while Windows looks in its restore points for a previous version. See sample below.
Previous Versions is NOT an alternative to normal backup.
Good info on what it is and how to use here ===>>>
http://www.howtogeek.com/56891/use-w...ve-your-files/
BR