Actually, their substantial diversification beyond Windows means that it's very, very unlikely Microsoft is going to fall (easily or quickly). Microsoft could lose the entire consumer Windows business and be just fine (despite the hit their stock would take), particularly as they keep growing in other sectors while Windows becomes less important by the day (and is clearly done growing as a business). Consumer Windows is about 1/3 of Microsoft's profit these days.

Apple by comparison gets about 3/4 of its profit from the iPhone. Google is even worse, 95% of their profit comes directly from search.