Halo creators Bungie may have signed a publishing deal with Activision, but let's not forget, there's always the possibility they can sign with rivals Electronic Arts as well.
Remember: Bungie's deal with Activision is for a single piece of intellectual property. With Bungie being a massive studio, however, there remains the distinct possibility it could become so big that, like Rockstar, it splinters and can work on several games at once. Should that happen, EA will be waiting in the wings.
"I don't want to see them fail - I want them to be successful", EA's David DeMartini told CVG. "And when they start up a second team, we'll have other discussions with them about that game as well - because they're a great studio. There are probably only 20 studios in the world that are that highest level - and they're certainly one of them."
Sounds like desperation on the part of EA, but I'd hope that if Bungie learned one thing from its departure from Microsoft, it's that saddling up with a single publisher for the long term can be a risky proposition. After all, the Bungie that signed the initial pre-Halo deal with Microsoft was a different Bungie to the one releasing Halo: Reach, and you'd think in ten year's time they'll be different again.