A few folks on this board have been considering the possibility of a Nink retirement since well before the draft. I personally thought it would be AFTER this season, but it is what it is.
I'm not really concerned about a 1-for-1 "replacement" for Nink, though. The roles of a few other players will likely be re-configured and probably would have been anyway this season, considering the differing skillsets (strengths/weaknesses) of the new players like Rivers, Ealy, Guy, Wise and Harris who have been brought in.
So far, Harris hs been showing that he has something significant left in tank. If he can lead the linebackers, that maybe frees up HT for more on-the-line edge work. Rivers looking reasonable in TE coverage perhaps indicates some consideration for him in a hybrid OLB/DE role, rather than as a pure, on-the-line edge guy, and maybe makes him the closest to a Nink replacement. Guy appears to be able to play the line outside or inside, and Wise may have some of the same ability, perhaps leaving Flowers as more of a pure edge-rusher with Ealy as a situational addition or relief man.
It seems to me that there's a lot of talent and potetnail versatility in this front-seven group, even without Nink. Just a lot of tinkering ahead to figure out where everyone best fits in the schemes and how those schemes can be variably customized and applied in opponent-specific ways. But then, there always is.