CINCINNATI -- It finally happened. And the city of Cincinnati couldn't be any happier -- or sadder.

In a young year that has already been full of conflicting feelings for the Cincinnati Bengals and their faithful, another emotional blow was levied Wednesday morning when ESPN's Adam Schefter and Chris Mortensen reported the Minnesota Vikings were hiring longtime Bengals assistant Mike Zimmer. At long last, Cincinnati's defensive coordinator since 2008 received the job he probably could have -- nay, should have -- been given years ago.

Zimmer is now a head coach. Let the growing pains begin.

The good news for the Bengals is that much like last week's hiring of former offensive coordinator Jay Gruden by Washington, they have been preparing for some time for this particular coaching change. And just like Gruden's replacement, Hue Jackson, the Bengals are expected to make the transition to their next defensive coordinator from within. Linebackers coach Paul Guenther could be elevated in the wake of Zimmer's departure, although recent reports suggest Zimmer and Gruden may want to court him for their defensive coordinator openings, too.

The Bengals won't want that to happen. To keep the growing pains down, they'll want Guenther.

If Guenther follows Zimmer to Minnesota, he likely won't be alone. Zimmer's son, assistant defensive backs coach Adam Zimmer, could be coming, too. The elder Zimmer credited Adam last week with being a key reason why the Bengals were able to weather a barrage of injuries in the secondary this season.

Whether Guenther, Jim Schwartz (a close friend to Bengals head coach Marvin Lewis), or someone else becomes the Bengals' new defensive coordinator one simple fact remains: An uncomfortable change is coming to Paul Brown Stadium.

Compared to Jackson's promotion, this next hiring ought to be viewed as a downgrade. No, that's not intended to be an insult to Guenther, Schwartz or whomever becomes the new coordinator. It's instead a compliment to Zimmer's work these past six seasons in Cincinnati.

Finding a carbon-copy replacement will be nearly impossible.

Many, including this ESPN.com reporter, praised the Bengals' hiring of Jackson primarily because he made such a strong emphasis in his news conference last Friday on doing the one thing the Bengals failed to do in their last three playoff appearances. He vowed to run, run and run some more.

What can the Bengals' new defensive coordinator do in the immediate future that Zimmer didn't already accomplish? Very little. After all, this was a defense that ranked as the NFL's fifth-best between 2008-13, and one that finished the 2013 regular season as the league's No. 3 unit for the year. That's precisely why Zimmer's replacement ought to be concerned with sticking to the same script of an aggressive, blitz-happy defense that has been a hallmark of Zimmer's coaching style for 14 years.

Minus defensive end Michael Johnson, who likely will be too expensive to re-sign this offseason, the personnel for a continued high-paced pass rush is there. So it ought to be maintained. If it is, the growing pains that will certainly come might be eased.

If you ask the Bengals, they'll tell you Zimmer's teachings are the reasons why they should thrive even after his departure. Not long after news of Zimmer's hiring was made public, Bengals linebacker Rey Maualuga issued the following message on Twitter.

Gonna miss you coach Zimmer! Wish you nothing but the best in Minnesota. You brought out the best (cont) http://t.co/6ytnHtHJ5C

— Rey Maualuga (@maualuga58) January 15, 2014

Along with Maualuga, the Bengals next year will have Pro Bowl linebacker Vontaze Burfict for a third season. Pro Bowl defensive tackle Geno Atkins will be coming back from ACL surgery. Veterans Leon Hall and Robert Geathers also will be back from major injuries, joining the likes of Domata Peko, Carlos Dunlap, Terence Newman and Adam Jones into the regular rotation. With the same defensive blueprint and near-exact replica of the 2013 team returning, the Bengals ought to get through this change.

But they should expect challenges.

Whoever takes Zimmer's job will have to have their voice respected right away. If it's Guenther, he suddenly goes from being just another voice in the coaches' meetings to the voice of record when it comes to the defensive side of the ball. If it's someone like Schwartz, he'll have to quickly win over the trust of every other coach and player in the room, even if the head coach already has it.

One positive the Bengals have in Guenther is the fact that he has proved an ability to take risks and generate maximum rewards off them. Case in point, the weakside linebacker who he, Zimmer and Lewis took a chance on following the 2012 draft.

Few teams were willing to take a hard look at Burfict, the former Arizona State standout who showed up to the NFL combine out of shape and overweight, and dealing with numerous off-field issues. Those factors contributed, in part, to him going undrafted. When undrafted free agents were permitted to sign, though, the Bengals were right there.

In short order, Burfict showed how much he trusted and respected the three coaches by becoming one of the top tacklers on the team as a rookie. Then this year, he led the NFL in stops. His growth and maturity were impressive. That's a credit to Lewis, Zimmer and Guenther.

That's why, if you're the Bengals, you hope everything works out with Guenther. Not only does he have pre-existing relationships, but he knows the terminology and system the Bengals like to use. He might not be Zimmer, but who is?

But at least with him on board, the growing pains might not be so bad.