Just circling back. Thanks for all the input! After doing some research myself, I concluded that it is best to have a '404 not found' page. If a search engine has a page that you have since renamed, it will cause some confusion if you have the 404 redirect to the main page. Also it will cause some confusion on the webmaster's part because you may not catch some bugs in your website because of it. When I built a 404 page, I quite quickly found some bugs on my website.