More to the point, how can you possibly know that the visitor has not taken any action? Maybe they came in through a search, found the information they were looking for, then left, as many do. So they did take action.
But there's no way to distinguish this single page view from one where they didn't read the page.
But as others here say, one sure way to guarantee that the visitor doesn't come back is to do an onunload event fired popup.
Also, XP SP 2 blocks popups, Firefox blocks popups, I assume Safari blocks popups, so what's the point in the first place?