Won't matter who they do or don't sign.
It's a poorly coached football team. Near the bottom in penalties, inexplicable playcalling, on both sides of the ball, lack of discipline all across the board. Having enough talent isn't this team's problem. Just go back a few years. 3 all-pro, potentially HOF caliber offensive linemen, yet when it mattered, we couldn't run the ball and win a playoff game.
The coaching is bad because the GM is bad. MM doesn't lead this team, Jerry & Steven Jones do. The players don't respond to coaching, don't really respect their coaches, because they know they aren't in charge. The players know what Jimmy Johnson said years ago is true: the real HC is Jerry Jones. Doesn't matter how many good players McClay drafts, this isn't like baseball used to be where Jerry & Steven Steinbrenner can buy enough high-powered players to win a title. If the Cowboys had, for example, signed Reddick, it wouldn't make a huge difference. Because this is a poorly-constructed ship, it will always spring a leak somewhere else, which guarantees come January, it will sink. 27 years of history says this isn't debatable.