Well, the book doesn't cover presenting without slides - assuming that you're thinking of the usual slide full of bullet points.
The idea it's promoting is to use more visual slides, that highlight the main point and possibly use an image (photo, visualisation, whatever's appropriate in the context) to support what the speaker is talking about.
So in that sense, these sorts of slides can't really be used as a "safety net" either. They're an outline of your talk and a backdrop, but the actual content is the spoken
word.
But whether you go with visual slides or no slides at all - you'll have to really think through what your talk is about and what your main message is. If you do that, and rehearse a few times, you'll find that you can easily present without having to look at your notes. You won't say the exact same thing every time, of course, but the content will be the same.
Does that help?
"Presenting for Geeks" covers the above for the use with slides as described. If you really intend to present without any slides, you may want to look for other books. "The Naked Presenter" by Garr Reynolds would be a start.