Hey,
I wouldn't try to reconnect a button that fell off. You would more than likely cause stress in the rest of the tail, and could cause damage to other buttons of the rattle. It would probablly fall off again quickly (should you ever get it on), and it would put serious stress on the snake to try to restrain it while you go about the attempt of tail "reconstruction". Taxidermists have reattached buttons using superglue, which works fine as the animal is dead and will not be using its tail! The rattle needs to be able to move in order to vibrate and produce that buzz we all love so much. Pushing the brittle plates together could cause stress cracks leading to further deterioration, or the rest of the tail to snap off in your hand!
Rattlers have been known to have a serious number of "buttons" or segments. Wild caught buzztails usually have less than captive raised ones as in nature they are easily broken by rough terrain, predators, etc. With that said there are of course exceptions...roundups often times have an award for any snake brought back with the most rattles. Usually the winner is from 18-23 rattles, but there are often times many more or less. I don't support roundups in any fashion, I am merely stating a fact. A lot of what we know about "record" snakes is not from collectors or hobbiests, it is information that was obtained through these horrid events.
My little norther pacific female (02 CH) has about 6 buttons now. She should have a few more, but she likes to soak in her water bowl, and has lost 2-3 in the process. She is in burmation now, and should form a nice new button upon her next shed (as soon as she is active and out of burmation).
-Steve Clark