I can already tell you how much of iPhone fans in my entourage won't buy the new iPhone and would stick with the 4S, or either get the Lumia 920
I don't think it's possible to wipe out iPhone, not anytime soon. Considering the following iPhone has, and most of them loyal, it'll take a long time before iPhone really gets damaged. There are plenty of Apple fans that'll stick to iPhone regardless of what happens. The main thing is, people are willin to shell out money for iPhone as long as it looks good and works as they want it to.
I don't think there's a clear-cut superior competitor for iPhone to really lose popularity, like how a Mac was a superior competitor to Windows.