With respect to the front seven, Nwosu is definitely a keeper. Wait and see on Brooks injury. Jury is still out on Mafe plus he is on the rookie deal.
Collier, Harris, Jefferson, Adams, Ford, Woods are probably not worth resigning and they are a collectively better group than the linebackers which I believe to be, by far, the weakest position group on the team. I am solidly in the camp that the team needs to draft a minimum of two "off ball" linebackers on day 2 of the draft and you wouldn't see me complain if they drafted two defensive linemen on day 1, however, I actually do think the edge position, as is, is serviceable. They just have to be more consistent "setting the edge" (ie. forcing backs towards pursuit help in the middle of the field) in the run game.
Therefore, you wouldn't see me complain about any free agent linebacker acquisitions (they don't really bust the bank relatively speaking). The team probably moved on from Wagner a couple of years sooner than they should have, but they probably thought Brooks could make up the difference and he almost did. For a while anyways. I believe there were occasions where he was leading the league in tackles or was among the league leaders. I will give Brooks the benefit of the doubt because the DT's were not helping him much at all. But now that he is coming off injury, there is a big question mark about him.