... no?
Vic Fangio, the 49ers' defensive coordinator, has not been mentioned in association with the Vikings job, from what I've seen. It was just reported that Minnesota would interview San Francisco's offensive coordinator though.
Fangio did interview to replace Mike Shanahan in Washington, but they didn't hire him. I haven't seen him linked to any other jobs. Even if he did go elsewhere, I believe there are other guys on their staff likely to get promoted internally before Leavitt, and that's assuming they even choose their next defensive coordinator from someone currently on staff. Their defensive backs coach, Ed Donatell, has been a defensive coordinator for both the Packers and the Falcons in the past. They also have an assistant named Peter Hansen who works closely with Fangio in preparing scouting reports, studying film, and other stuff; he filled the same role working with Fangio and Harbaugh at Stanford, and Harbaugh supposedly has a very high opinion of him.
http://espn.go.com/nfl/story/_/id/10277775/minnesota-vikings-interview-49ers-offensive-coordinator-greg-roman