They have just under a year
... to realize that a lot of businesses are still running XP and are quite happy with it. When they kill XP, they imagine all those businesses will upgrade to Windows 8. HA bloody HA!
Ok, there's Windows 7, which is perhaps less painful. Even so, lack of drivers will obsolete a lot of hardware, and lack of RAM will obsolete a lot of PCs. And there's no real upgrade path. MS say you should upgrade to Vista and then from Vista to Windows 7. Sorry I feel another attack of graveside laughter coming on. Even if it worked, how many extra man-hours will that consume?
Given the requirement to tear it all up and start again, how many will stick with Microsoft, and how many will go to Apple? Some may even find time for Linux. Those that do stick with Microsoft are unlikely to bear any goodwill for Microsoft in the future. Sooner or later someone will ship a Linux derivative for business use (just as Google shipped a Linux derivative for handset and tablet use: Android).
So what they have to do now is simple. Announce that XP will continue to be supported until an idiot-proof upgrade to Windows 7 is developed. And annnounce that you'll never have to learn a new interface because the Windows 7 one will be maintained in perpetuity (ie Windows 8, Windows 9 will have a "Windows 7 style" option). Ditto Office.
Oh, and to make money stop selling perpetual Windows licenses. That way you won't have to keep shredding old Windows in order to force customers to use New Windows. You'll just charge them renewal fees for continued support of what they want. Of course, it would help if your customers trusted you more than they trust a low-end used-car salesman. Sacking the CEO might be a good start, followed by a new CEO eating humble pie.