Do not strand them
Stranding users is not a good thing to do, I think we can all agree with that premise. Not remembering that a user of your site can drop in to the site from anywhere to anywhere can be fatal. Take the U.S. Treasury Department, which recently did an expansive redesign of their site. They did a good job at bringing together much of their domain under one consistent branding roof. They have a few large navigation problems, they tend to pop-up a new window at the drop of a hat. Worse is that many of their press releases are built to pop-up, but have absolutely no navigation, not even to the Treasury homepage. I was suckered by this in July while searching for information from Google I was dropped in to a press release with nearly the exact information I was seeking. Big problem, all the Treasury Press Releases (sample of poor Treasury Web design) have no related links and no navigation to get you to the sourse of the page. When the Treasury gets around to fixing the stranded user problems they created they should fix the giant top banner/navigation bar that keeps the information their users are coming to the site for pushed down the page.
I will give the Treasury large kudos for grasping control of the splintered branding that is rampant in the large organizations. This consistantcy provides a couple of advantages by providing ease common design that give welcome consistancy and it makes it easier to go back and correct the navigation and usability errors that were left behind.