Well, it took a bit of research plus tips from Mumbles, Jon Bell and John Tantalo, but here goes:

myth.godgames.com is no longer active. myth3.godgames.com is still active, and redirects you to http://www.godgames.com/main.php?section=gamers&game=myth3, as it did before. However, this isn't a permanent page, but rather the output of a script; go to http://www.godgames.com/main.php?section=gamers&game=[randomstring] and you'll get to a page with the text [randomstring]. Wasn't that fun?

So to summarize, GOD doesn't have a real page up for Myth3 yet, but myth3.godgames.com redirects to a faux one. :-)