Just think about what Mike Zimmer was able to do with Adam Jones and Terrence Newman. Zimmer spent his first 6 season in the NFL as a secondary coach. He was able to retread some players and make them key parts of a Bengals defense that finished in the top 10 four times.
It wouldn't be a shock to think the secondary of this defense may change without a leader like Mike Zimmer. But, the Bengals thought of that too. The guy that was brought in to fill in as a secondary coach is looked at as a hot up and coming defensive minded coach. Vance Joseph also built quite a secondary with the Texans and is a welcome addition to the Bengals.
When Houston was making their playoff runs these past few seasons, the secondary play for the Texans was pretty outstanding. The Bengals even talked with former Bengals Jonathan Joseph about his coach and he had nothing but positiver things to add.
So while it may seem like the Bengals have lost a lot in Mike Zimmer leaving, I am confident in the guys they have brought in as well as the culture that Zimmer leaves behind. I think this defense is ready to pick up where it left off last season, and that is a great thing.