I think you simply let 2018 play out on the field (don't pick up the option) and the decision may become easier.
The money being spent on Dareus, Campbell and Jackson is prohibitive.

The first and easiest way to help find a way to keep Fowler (and still re-sign the more obvious keepers of Jack/Ramsey/Ngakoue) is to move on from Dareus in 2019 when the "out" in his contract comes up.
That likely means going all in on a run stuffing DT/NT in the 2019 draft (unless they surprise us and draft one next week.)
Campbell, who will be 33 by week one of the 2019 season, also has an out in his contract after this season. Will he show any signs of father time nipping at his heels? Does Smoot flash enough this year to give us confidence to move on?

There are just too many unanswered questions for me right now to want to deal Fowler away. I'd like to find a way to keep all of the contributing young players on this defense and I think saying goodbye to a vet (maybe two) and replacing them with draft picks may be all that is required.

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