I'm assuming you have the "Lid close action" in the chosen Power Profile configured to "Do Nothing". If I were in your situation, I'd try troubleshooting by creating a new Power Profile, setting the "Lid close action" to "Do Nothing" and see if you can reproduce the WiFi shutdown behavior. If you cannot, it could indicate your other Power Profile is corrupt, and a Reset/Reconfigure of it may provide a solution.
Are you running Power4Gear to manage your Power Profiles?
I don't have Windows 8, but I read there is an "Airplane Mode" utility to turn off WiFi like on a cell phone. It may be worthwhile to check if you can make any configuration changes there.
Yours sounds like another "Lid Close" issue thread (see
http://rog.asus.com/forum/showthread.php?7900-G53JW-Sleeping-While-Gaming-Overheat&country=&status=) where the user reports his laptop goes to Sleep during gaming when he closes the laptop lid, even though it is configured to "Do Nothing" in the Power Profile.
G74SX-A1 - stock hardware - BIOS 202 - 2nd Monitor VISIO VF551XVT