If no one releases a popular web browsing platform that lacks Flash support, then web sites that already publish Flash content are never going to move away from it. I think the web would be a far better place without Flash, or, at least, with Flash relegated to a position like that of Java applets: there if you want it, but not a major foundation.
Flash is never going to decrease in popularity so long as all web browsers support it. Flash might decrease in popularity because of iOS. If you believe that Flash’s current position as a de facto standard technology is harmful to the web, then users — not just iOS users but everyone using the web — would benefit if that happens.