Activision will be just the publisher for the Bungie games that is all....I mean Bungie can take so long they want to make a game..
The deal with MS has hurt the Halo games, the first game lacked online multiplayer because MS couldn't make the service on time, Halo 2 had a deadline and a lot of stuff has been cut, two covenant races didn't made , and a few stages aswell (that is why Halo 2 is in the history books as one of the games with the most horrible endings) Halo 3 normally would have firefight but then again MS pushed them to deliver Halo 3 sooner etc..