The only time you can "break" the Wifi toggle is if you're on a jailbroken 4S on iOS 5 and using SBsettings. After a certain amount of toggles, the toggle becomes unresponsive so you'll have to respring to get the toggle working again in SBsettings or manually toggle in Settings. Apparently it's a known bug but there's no clue on how to fix it. As for a stock 4S, nope, can't break the toggle or your Wifi