Maybe...
... if Microsoft hadn't been such greedy sods in demanding the same 30% cut as Apple did for entry to their app store, Windows Phone might have stood more of a chance. Or if they hadn't ended up appearing so weak by having to pay devs to develop apps for it. Or if they hadn't tied developing Windows Phone apps to a forced upgrade to Windows 8 whether you wanted to or not. Or if they'd curated their app store better to keep the fart apps out. Or...
Nadella can play the "well, it wasn't my idea" card as hard as he likes and claim that markets always tend to converge on two dominant players anyway, but the fact is that Windows Phone didn't have to fail quite as hard as it did. That's all down to the pathological political situation that prevailed in Microsoft in the latter years of Ballmer's tenure and which still hasn't been fully resolved: witness the mass exodus of talent into the cloud services arm of the company in search of shiny things leaving the OS and desktop applications sides of the business apparently bereft of all adult supervision.