Unfortunately, the press release from MS makes it sound like Bungie's not quite free and clear yet. Microsoft expects Bungie to keep developing Halo, and working with them on future Halo-related projects. But that could be Microsoft just trying to look at things through rose-colored glasses. Or then again, it might not: the official word from Bungie is that they remain partners, and "nothing has changed." What a shame.
My official guess (TM) is that Bungie will release a brand new intellectual property, and that it will arrive not only on the Xbox, but on other consoles as well (possibly including the Mac, but let's not count our chickens before they hatch). For all their talk of a split, Bungie still isn't as independent as it once was. Microsoft is still in the picture, and it's pretty unlikely that Bungie will go back to developing specifically for the Mac again any time soon.
via x3f -- thanks to everyone who sent this in.