You have to look at these coaching changes as an opportunity. Coaches aren't going to be around forever especially if they have success.
You could argue that our secondary was the weakest part of the defense this year so was that coaching? On recruiting neither landed a 4 or 5 star recruit so maybe the next two are even better recruiters. My point is there is always room for improvement. You prefer that to happen organically, but sometimes change is good.
Let's see who they hire before worrying about who they lost.