Kevin Williams isn't that old and hasn't shown signs of slowing down. Pat is on his last legs, but quietly Jimmy Kennedy is starting to steal more of his snaps. He's really enjoying quite the renaissance in Minnesota and has turned into a good player.
The linebacking corps is one of the best in the league and Henderson and Greenway are both pro bowl level LBs. Leber has been slowed with injuries this year and may be due for replacement, but otherwise that's a unit with life in it.
In the secondary Griffin is injured but still relatively young and that's not an injury that should have a lasting impact, and while Winfield is up there you have to remember there's a lot of youth at the corner position as well with Cook and Asher Allen.
Frazier will probably move on soon but they won't have trouble bringing in a quality coach to replace him, and there's plenty of talent to work with and ownership that's not shy about giving them money to work with.
I don't mean to paint a bleak picture of the Vikings -- I think the defense will still be solid but I think there will be attrition due to age, injuries and departures. Williams is not a nose tackle type like Pat Williams (who actually got better with age), he is a penetrating, disruptive DT and his numbers have decreased over the years. I realize part of this is a result of double teaming etc. but I don't think he will be as effective a player as he is getting older. I think we will really miss Ray Edwards.
I agree that Jimmy Kennedy has been a VERY solid player and I think we will hardly miss fat pat when he steps in (hope he sticks around; he has been complaining a lot recently).
Greenway is only 27 and has plenty of life left in him. Henderson is 30 and I'm afraid injuries have taken a toll...still a few good years left, though. Leber is likely moving on after the season, from what I've heard.
The secondary is what worries me most. Cedric is young, but he has had two ACL tears now. Winfield still looks good against the run/tackling, but the coverage skills are lacking. I'm not sold on Allen or Cook, yet, but they still have plenty of time to prove themselves -- they just aren't known quantities. Not a big fan of our safeties at all. I think the secondary is our biggest weakness.
Once again, not saying the Vikings D is about to fall apart but I don't think they have the pieces to be as elite of a D they have been the last couple of years
If Frazier takes the MN job, he doesn't have to move (not sure if he has any kids other than the one that went to Rice), and he gets a big time job, although not an NFL job. I really wouldn't mind if he moves on to an NFL job in 3 years, because that means he is having success here. I would rather have success but discontinuity in our coaches, than having continuity and not win.