As previously noted, Microsoft owns Bungie, so it is impossible that the developer would be able to split from Microsoft without Microsoft's desire to sell it. The latest round of industry gossip addresses this issue.
According to a source quoted by Game Informer, Bungie shareholders supposedly brokered a deal allowing them to buy the Bungie name back from Microsoft as long as the corporation has "the right of first refusal" on all future Bungie titles.
If true, Bungie would have to pitch new titles to Microsoft before they approached any other publisher. Such a setup would guarantee Microsoft the first pick at potential blockbusters but would also allow the studio more freedom, including the option to develop on other platforms.
However, the notion of Bungie having shareholders struck some the wrong way, especially since Microsoft acquired complete ownership of the studio. For clarification, Shacknews inquired to a Microsoft representative, who responded with "we don't discuss financial terms."
The report also specifies that Microsoft would retain ownership of the Halo property--undoubtedly the rumor's most believable aspect.
Other speculation has key staff leaving the studio and either forming a new company or joining an existing one, perhaps one founded by a former Bungie employee. Bungie founder and Halo creator Alexander Seropian went on to form Wideload Games. Bungie alum and Halo 2 online lead Max Hoberman presides over Certain Affinity, which recently developed the Blastacular Halo 2 map pack.
As both Microsoft and Bungie continue to dance around the rumor, and as Bungie employees are generally quick to comment or at least touch on breaking news, it is seeming more and more likely that something is indeed transpiring behind the scenes.