Redirecting certain 404s to a page, handling all others as normal
You could also set up a route for news/{slug} to point to your news template, and have it do the check to see if the entry in segment_2 is valid, and do something based on that.

I did something like this for my "members" pages:

 {% set thisProfile = craft.users.id(craft.request.segment(2))[0] %}

 {% if not thisProfile %}
    {% redirect siteUrl %}
 {% endif %}