If a journal announcement has expired (or been deleted), the notifications page (accessible via the "view" link in the notification block) displays an entry with "Go To URL" pointing to an inaccessible page.  Similarly, the announcement RSS feed continues to display a link to the deleted announcement, which generates a 404.

If the announcement is not accessible, the link should consistently redirect to the journal announcement page or somewhere similar, if it is shown at all.  It occurs to me that the simplest approach here may be to add a journal-specific 404 handler as part of the creation of each journal or to change the web server installation instructions appropriately, so that all uncaught 404s would go to the journal front page.

By the way, I'm also not convinced that editing the text of an existing announcement should generate a new notification.  We had one editor who couldn't get the text right and edited an announcement a half dozen times in a few minutes, which generated lots of complaints from readers who had signed up for email notifications.