I'm not completely sure, but I believe that if the change-after-listing is done purposefully ("bait-and-switch") that the site will be banned from ODP.
If the domain for the site got bought up by one of those domain resellers that put affiliate link directories in their place, we'll try to find the new location for the site, and delete the entry if none can be found.
If the site got bought by Acme Corp, and redirects to their already-listed-in-ODP website, it will get deleted.
If the site owner, for whatever reason (besides bait-and-switch) decides to change the focus of the site, we'll move the listing to a more appropriate location.