I think Fangio's "style" can be replicated to some degree. Now, there is a lot more to Fangio than style, let that be clear. But, getting quality players through the draft that fit the 3-4 defense is about all the Bears can do. Fangio could easily find a HC job but, IIRC, didn't even interview. So, maybe, he is content for the time being. Or, maybe he jumps ship after this year. I don't think anyone other than Fangio and maybe Pace and/or Fox know what Fangio is likely to do. So I think you go get the best players that fit the scheme.
I don't know whether one should put the "who is responsible" on either Fox or Fangio. Right now, like it or not, Fox is the HC and they should get players that Pace and he likes with as much input from Fangio that they trust. At the end, getting any talented player that fits the 3-4 is a good thing and I would think that would be what they will do. The defense will get better this year. Throw in a FA or two and a couple of 1-3 round draft picks and we should see some significant improvement.