Resources not found in the application are actually handled by the container (the JBoss server in this case) not by the application. So, you need to handle it the way the container expects, via a web.xml directive:
<error-page> <error-code>404</error-code> <location>/error/404.html</location> </error-page>
You can redirect to a static page or a seam page.
Thank you very much for this idea. I will do this.