I wouldn't say Seymour is in the drivers seat. He's in something like temporary front row seating which was all the Patriots were willing to give him as a compromise 4 years ago for a couple of reasons. He was hurt a lot, he doesn't play well hurt, and despite his acknowledged talent he's never developed into the all in team leader they hoped he would. I think whether or not he stays is truly more their decision than his. And I think they may be somewhat ambivalent heading into his contract year depending on what he wants.
They won't pay top tier money for talent alone, it has to be part of a value added package that includes a more expansive team first leadership role. As Pioli used to say they gauge how much a guy wants to win championships here as opposed to his desire to simply get paid what he believes he's worth based on talent or past or present performance. Because you can only have so many top tier players earning top tier money within the confines of a salary cap and within the parameters of this system before you have to start cutting corners on the support system that benefits them all.
It will be much the same calculation for Wilfork as well as Mankins. Are they impact players on and off the field or can a similar impact be achieved by replacing them with one or more well coached albeit arguably less purely talented players given the level of their contract demands...
In the case of Brady the answer is pretty clearly no, but then he tempers his demands which make that decision a hell no. I think they hoped that Seymour would become that core player on defense, leading by example on and off the field, but the jury is still out. I also think that part of his 3 year $30M extension was an understanding that they would not revisit the matter until 2010. Hopefully the understanding didn't include any discussion of the franchise tag. Because with it the team truly remains in the drivers seat.