Surely, the original contract would contain a clause to discourage this eventuality, e.g. "If Bob allows a copy to be made, he hereby requests to be hung, quartered and drawn." (Which incidentally is probably where today's punishments for copyright infringement seem to be heading.)
I doubt anyone would agree to those terms since there's always the small chance that Bob could be the victim of theft or fraud. The only way it would work is if you included a clause that it must be intentional. Proving intent would be pretty difficult.
Then there's the loss of goodwill towards doing business with someone that reserves the right to torture/execute you. Who writes a book that is that good?
Also, if Bob is the only buyer of Alice's book, it's fairly obvious who leaked it. When Alice sells millions of copies, which is the point of copyright after all, it becomes a lot harder.