All once had close ties with Ballmer and the board but left -- Sinofsky most recently after shipping Windows 8. Of these three, Elop seems the most likely "outsider" for the board to tap. He has family still living in the Redmond, Wash. area. He's probably had enough fun running Nokia in Finland. He left Microsoft under the best terms. And he's not associated with a big money-losing division that the board might be now under pressure to sell off (Online Services, where Johnson hung his hat).
4. Mark Hurd of Oracle (ORCL): To me, the smartest move Microsoft could make here would be to double down on its enterprise business units and spin off or sell its Xbox and Online Services units. If it were to use the leadership change as an opportunity to push that idea, I think Mark Hurd would be an ideal candidate to run the new enterprise-focused Microsoft. It is right in his wheelhouse, plus it would give him the chance to stomp all over HP. However, in the process, he'd have to stomp all over Oracle as well. Therefore, Larry Ellison is likely unwilling to let Hurd walk -- and will pay him to keep him put.
5. Scott Forstall, formerly of Apple (AAPL): Forstall is looking for a new gig and he's from Seattle. If Microsoft wants to put an emphasis on its new phones with a big name, Forstall fits. But there's no way Microsoft would pick him to run the entire company. He has zero enterprise experience. The only way I could see him coming in is if the board decided to bust up Microsoft into a bunch of "Baby Bells" and appointed him to head the Windows Phone group. But busting up a company that radically is something a regulator does, not a board of directors.6. Satya Nadella, Kirill Tatarinov or Terry Myerson: Think about this: Microsoft's Business, Server and Tools, and Windows divisions accounted for 82% of its sales in the last year and 101% of its profit (because Online Services lost more money than Xbox made). Nadella's been there since 1992 and is now responsible for Microsoft's "Cloud OS" which has been a big winner for the company. Before that, he ran Server and Tools, a big feather in his cap. Myerson runs Windows, which is now seen as a fading cash cow. Tatarinov has had a shorter tenure with the company to likely make him seen "ready" by the board for the top job.