This may seem infeasible and/or culture-prohibitive, but there's another way Microsoft could go, which could see them gaining market share in mobile, and perhaps even surpassing google/Apple eventually.
Instead of trying to figure out how to optimally leverage the technology and assets they currently have (Nokia, Office, Windows Phone, patents, etc.) to optimize their own profit, as they have been doing for the last decade or so, they could try something new: building something which actual customers want. I know it's somewhat unheard of in the age of big companies, patent portfolios, and quarterly reports, but anyone who think there's not substantial room for innovation in virtually all aspects of the mobile space is simply not trying to think.
Microsoft had (and still has remnants of) the technical might to pursue multiple avenues of innovation at the same time. If they could simply change focus away from brow-beating their reluctant customers with their latest profit-optimized business plan, and toward giving customers what they actually want (here's a free hint: a phone where you are in control of where your data is, and what apps can access it), they could still do quite well. If they continue their current business mindset, though, it won't matter what they pick to focus on: eventually, they will be toast.