Again, to keep this from happening in the future,
back up your books. I suggest Dropbox, it is easy to use and I can shamelessly give you
my referral link 
to sign up if you don't have an account already. (We both get a 500MB bonus if you use it.)
Then simply put your library in your Dropbox folder and it will be safe from accidental deletion (you get thirty days to undelete stuff from the Dropbox website).