PITTSBURGH -- It finally looks like the end of an era for the Pittsburgh Steelers.

The Steelers appear poised for a complete overhaul of their defense, following the resignation of defensive coordinator Dick LeBeau. It's an overhaul that has been ongoing since 2012.

The departure of LeBeau, who wanted to return for another season, all but assures outside linebacker James Harrison, defensive end Brett Keisel and cornerback Ike Taylor won't be back in 2015.

The departure of Dick LeBeau might signal the exit of several prominent defensive players. Ronald C. Modra/Getty Images

It will also be a surprise if strong safety Troy Polamalu returns for a 13th NFL season. Polamalu, after Pittsburgh's loss to the Baltimore Ravens in an AFC wild-card game, said it is fair to question whether he has played his last game for the Steelers.

The departure of LeBeau might be a tipping point for Polamalu, if the eight-time Pro Bowl is still mulling his future.

That is how beloved LeBeau is by his players and how much his exit will sting for them.

The Steelers, however, were in a near-impossible position as long as LeBeau wanted to continue coaching.

The Steelers could not keep linebackers coach Keith Butler -- long believed to be LeBeau's successor as the team's defensive coordinator -- waiting forever, and at some point someone other than Dick LeBeau was going to coach Pitsburgh's defense.

If the decision not to bring LeBeau back for another season has anything to do with an organizational belief that his coaching has slipped in recent years, then shame on the Steelers.

The 77-year-old LeBeau defies birth certificates and conventional thinking about age. He inspires his players, who hated to fail him because they felt they were letting down their own fathers.

That is his legacy as much as his zone-blitz innovation and his Pro Football Hall of Fame playing career with the Detroit Lions.

LeBeau is probably as proud of the personal relationships he developed with his players as he is of what he accomplished on the field. Under LeBeau, the Steelers set the standard for NFL defenses while playing in three Super Bowls from 2005 to 2010 and winning two of them.

The Steelers, as much as they embrace the family atmosphere that has been cultivated inside and outside of team headquarters, are also known for making tough decisions. They have cut ties with iconic players going back to the early 1980s (see running back Franco Harris).

They rarely, if ever, let sentiment override business. That approach is what has made the Steelers one of the NFL's most successful franchises and the only one to win six Super Bowls.

It also led to the tough decision to move on from LeBeau, who might have deserved better and in a perfect world would have left on his own terms.