I think when KF hangs it up, so will PP and KOK. Phil has been given multiple offers in the past, as I remember a few years ago either he or KF mentioned as much in an interview/presser setting. As others have stated, I don't think Phil is a kissing hands and shaking babies kind of guy. I think he truly loves what he is doing as an X/O kind of guy, that keeps churning out pro players.
I have a feeling BF will end up being the next head coach, and KF may well take on a "special advisor" role with the OL even after he calls it a career, similar to what his mentor, Joe Moore did. I also agree with the previous poster, that Copeland may well be being groomed to take over as OC in the future.
Many other posters in addition to myself have posted that Brian's offenses have to finish consistently higher in the Big Ten rankings before he should be considered for the top job.
You want to hire an offensive coordinator to be head coach? Fine. Show me some really good offense (consistently) that makes you deserving of being a Big Ten Head Coach.