I don't see Belicheck coaching another 9+ years, I agree that I think he has a few more left. Brady probably plays another 2, maybe 3 years after this year. Belicheck either leaves when Brady does or stays one more year just to prove to everybody it wasn't Brady, but he doesn't stay for 9 more years.
I read an article on Bellicheck a couple of weeks ago. Basically said that besides being a football savant from growing up with a father as a coach, the other reason BB is so good is that he outworks everybody and only surrounds himself with people that do the same. There was a coach who talked about how he sat down with BB for the first time when he joined the staff and they had the next team's game film. BB sits down with him and proceeds for the next hour to start at play one and go over everything he sees and wants in the notes for the next game. It took him an hour to get through 3 plays he was so thorough. Then he tells this coach that he needs the whole game film done by Tuesday morning meetings, it was Sunday morning when they did this. This young coach quickly did the math in his head and figured out he had 20+ hours of game film based on 20 minutes per play to get done in less than 48 hours and that was in addition to attending practice and coaches meetings, etc...ie, BB expected him to work 14+ hours per day. He said he did it and did it every week the rest of the year. Said BB doesn't matter how talented you are or not, if you are not willing to work and follow his rules, you are out. So the entire organization is fully in sync with the program.