First of all define Big Money. The franchise DT rate is only $6.5 million or so. So Wilfork on a long term deal $5.5 million+.
But to your real question. No I don't feel Wilfork is irreplaceable. He is good but not necessarily a HOF player. We have won championships with other NTs, Seymour, (yes Seymour), Washington, Traylor, etc.
There is an irreplaceabl player on the roster. There are a lot of people who are un-informed who seem to think a "Foundation" Defensive lineman who wil go directly to Canton like all the other foundation linemen, Alan Page, Merlin Olsen, Bob Lilley, Dan White, Dan Hampton, Reggie Wright is easily replaceable by some clod drafted in the third round. And we have such a player. The highest draft pick Belichick has made with the Pats, Richard Seymour.
Whether I would keep Richard Seymour is beside the Point, Bill Belichick will. He knows that Seymour stops the run just as much as Wilfork or more.
Bill also knows that Seymour provides ALL the interior defensive line pass rush for virtually the entire three man line. Belichick knows the Seymour IS irreplaceable and will pay and re-sign him, for about the money he is currently making, with a small boost.
He also knows that is the same money the Haynesworth actually as opposed to theoretically, will get. Seymour is finishing up on a 4 year $40 million deal. Haynesworth just signed real $41 million 4 year deal, advertised with never to be seen options, to make it an 8 year deal for $100 million.
incidentally, Belichick wil slit his wrists before he will let either go, I believe. He'd cut half the team to find the money. He knows how you build a Defense.