The Bengals lost both Zimmer and Gruden, and while they have very good coaches stepping up to be coordinators, including Hue Jackson on offense who was a head coach and coordinator before, that's quite a loss for any team. Zimmer was the heart and soul of that defense, and Mike Brown drafted the offense based on players Gruden wanted for his offense, so it remains to be seen how much those new coordinators change things. The Ravens should also be improved in the division, and you can't count out Pittsburgh either.
The Chiefs lost 3 out of 5 starters along the offensive line, and that is a huge loss. They also lost one of the best return men in Dexter McCluster, who was also used in a variety of ways as a receiving threat for KC. They also missed out on Emmanuel Sanders to replace McCluster and upgrade WR, but it seems KC will still trot out Dwayne Bowe and many no-name receivers. They also lost a good run-stopper on the line in Tyson Jackson. I don't think the Chiefs go back to the bottom of the league, but they are an between a 7-9 win team right now.
The Chargers are going to really miss Whisenhunt, although McCoy is an offensive guru in his own right. Their biggest FA addition was Donald Brown, given $4 million guaranteed, at a position where they have Ryan Matthews and Danny Woodhead. The Chargers still have holes to fill at CB and the interior line positions, and will likely need to work on all through the draft. I just didn't see this team get any better anywhere, and they already had to ride a hot streak and luck to get into the playoffs.