If your requirement is that the user cannot change the notebook options which implement what you need, then I think that the general answer is that it cannot be done. But, that said, there are all sorts of ways to implement a way to either make the notebook not savable (as you suggest) or to have something that can reset the notebook back to its original state as desired. E.G. have a button in a docked cell that has the contents of the notebook in it (which of course doubles the Byte size of the notebook) and which, when clicked on, deletes the contents of the notebook and writes the original material back. Not a terribly good idea, but you get the drift

If you look at the Documentation Center notebooks directly you can see that they in fact have the option setting

Saveable -> False