Former Xbox chief Don Mattrick left his post at Microsoft and joined Zynga as the company's new CEO. This left a vacant hole over at Microsoft, for which CEO Steve Ballmer is currently stepping in for the time being. However, it's been reported that current Windows head Julie Larson-Green could be the successor to Mattrick and take over the Xbox division as well.
According to Bloomberg, Microsoft is said to be in the planning stages of reorganizing the company's execs, and Mattrick is believed to have left Microsoft because of that. As for who will do what, it's said that Skype president Tony Bates will be put in charge of acquisitions and relationships with software developers for Microsoft, and Larson-Green will oversee all hardware engineering for the company.
This means that Larson-Green would oversee hardware engineering for all devices, including Xbox consoles and Surface tablets. Furthermore, Windows Phone software chief Terry Myerson would be given more responsibility, and will oversee Windows operating system engineering.
Sources say that these shuffling moves aren't finalized, and it's possible that Ballmer will make changes before Microsoft officially announces the reorganization. This means that it's possible that Larson-Green won't end up getting the Xbox division under her authority, but seeing as how the Xbox One is merging ever so closer to the Windows platform, it makes sense to put the two together under the same boss.
As for Mattrick, it's said that he was a contender for the hardware chief position before he left Microsoft, but knowing that the company would be going through a reshuffling, Mattrick probably didn't want to get caught up in the changes. Of course, Mattrick isn't heading to any steadier waters, as he'll be responsible for picking up the broken pieces of Zynga and trying to put them back together.