Straight Answer is No.
iOS as a mobile operating system, is, to me, the leading OS in terms of fan base and users. Yes, I know that Android makes up the most amount of marketshare and is on more devices than any other OS, but for me the market leader is still Apple.
In terms of Windows Phone, don't get me wrong, i'm as passionate as anyone about the platform. But, the OS still has maturing to do. I've had a device since WP7 (The Omnia 7) and it's come a long way. But, it isn't done yet, nor is it even close to "killing off any other OS".
As stated in other comments, competition is definitely a good thing. I feel as though Google, Samsung (as the leading manufacturer of Android handsets) and Apple are both jumping on the latest hype train and not being creative, but being "Gimmicky" in a lot of ways. Some innovation is shining through from these guys, but they are really lacking creativity. Anyone who has seen the Galaxy S5 and the latest iteration of the Android OS knows what I'm getting at: Boring.
This is where WP steps in. Creativity is coming in waves. Whilst it is helping WP's market share, there is still a long way to go but it is these new ideas and creativity that we are seeing that is slowly making it hard for Blackberry to come back. Blackberry dropped from 4.1% marketshare to 1.7% over the last year. I dare say that has to do with Windows Phone is some regards..
Anyway as long as you enjoy YOUR smartphone and YOUR phone is what you want it to be, then that's all that matters. Everything else will just fall in to place as long as Microsoft continues it's push.