If Android magically evaporated tomorrow Google would be just fine -- the core of their business (ad sales) doesn't fundamentally require that they control the mobile platform, although it certainly makes things easier.
Microsoft, on the other hand, had for decades been the platform company. They've historically tried to grow by pushing out from their desktop beachhead into other territory they think they can control the platform for (i.e. servers, game consoles)
Now suddenly they've found themselves behind in the highest-growth segments of the industry. In fact, just "behind" doesn't do their situation justice: they've had to spend billions just to claw themselves into a distant third place.
I expect that those billions will keep flowing. Microsoft is desperate to win this thing.