Word from Microsoft came as a surprise for the studio, which felt it was "immune" to being shuttered
Earlier this month Microsoft Game Studios confirmed it would be closing down Ensemble Studios, developer behind the Age of Empires franchise, in order "to spend the development dollars in other places" and keep MGS "on its growth path". The Ensemble Studios website has been updated with a brief farewell notice, and some members of the team, including company founder Bruce Shelly, also leave some parting words in their community blog postings.
Shelly in particular greatly regrets the decision MGS was forced to make; the official word of their closure surprised him, especially in light of their profitability and success over the past twelve years. Combined with a stable team that faced low turnover, he believed Ensemble was " immune to shut-down talk". His own take on MGS' position boils down to three key factors:
First, they want to divert the headcount tied up in ES and the costs that are expected to be required to run ES for the next few years into other projects. Second, it sounded like it cost more to run ES on a per person basis than other first party studios (Rare, Lionhead, Forza, Flight Sim) putting us at a disadvantage. (Plus they avoid the expense of a new office that we were planning.) And third, games those studios are expected to deliver in the next few years are expected to be more strategic and profitable to the company than anything we would be finishing after Halo Wars.
Halo Wars will be the last title which Ensemble, as we know it, will be working on. On the bright side, Shelly expects no layoffs at the studio before the game is finally released by the end of this year. As reported earlier, Ensemble will be forming a new independent studio following its closure, and current members of the team are invited to become a part of it. We'll have to wait and see what this upcoming studio has in store, but Shelly himself does not expect to be a part of it.
Update: Gamasutra writes that Ensemble had another Halo-themed title lined up for Microsoft in the works, but was eventually cancelled. Interestingly enough, this title was expected to be a Halo MMORPG. They even managed to snag some production screenshots; one example came complete with the UI.

I guess everybody would've wanted to become a Spartan had this seen the light of day.