It is confirmed that Microsoft will be dissolving Ensemble Studios as soon as Halo Wars is completed. Apparently, Ensemble’s top shots will form a new studio that will "work on other projects with Microsoft Game Studios."
Ensemble has been in Microsoft’s ownership since 2001 and has since raked in some serious dough with Age of Empires and Age of Mythology.
Microsoft claims that this decision has nothing to do with Ensemble’s talent or the upcoming game’s quality, as the game reportedly has good chances to become a hit. However, the decision is of fiscal nature and should “keep MGS on its growing path.”
More here.