You can participate in Google AdSense for as long as you wish, and you can cancel at any time by removing the AdSense ad code from your website pages.
I have just been accepted by adsense, and am wondering, given the above quote, if the code disappears are you automatically quitting, and, if I take a day or two (or a week) to add the code, am I at some point removed from Adsense?
This may sound silly, but the above quote is a bit ambiguous or vague...
I think Adsense would clarify what constitutes removal from the program before they would do that simply because there is no code being served. If you feel the language isn't clear, you should direct your question to Google, but I would not be concerned about it at all.