Free agent linebacker?
For the most part, Cowboys have not shown they can make good free agent decisions on key players. Cooper was an exception, but he's an offensive player. The Hardy, Thornton, McCoy, Poe, etc. moves were more in line with how it's gone the last few years.
So I don't want them to "fix" linebacker with a free agent.
Really I think who, or what position, they take will depend mostly on how it goes in picks 1-9. Obviously some positions you seldom draft anyway, like punter and kicker. Some can't be upgraded early in the draft, due to cap ramifications (i.e. Zeke) Some positions are fine as is, not that you don't want to improve, but their group performance is sufficient as is (i.e. receiver). Some you can take a chance on (i.e. tight end, if Jarwin is recovering well, and OT, ditto Collins and Smith, and OG, ). And some positions don't have the really "sure fire", as far as ratings go, players in the draft (i.e. DT). And of course if you believe what Jerry is saying, Dak will be the quarterback, be it with a new contract or tagging him again. So quarterback is off the list.
So what position player you might take early can be (if you want to follow the above view) winnowed down to LB, S or CB. Pretty good bet one of those positions will have a top player available at no. 10, likely 3 quarterbacks will go it the first 9, leaving only 6 picks before Dallas' pick. There are 3 very good LB, 2 very good CB and 2 very good safety prospects. That's 7, no matter how the other 6 picks go, Cowboys can clearly grab one top prospect, and for me, any of the 3 positions will help this team.
After that, your player evaluation and drafting skills come into play, and yes some luck, like Diggs being available in the second round last year.
Of course the Cowboys can screw up the draft, they've done it before, but that's not because of available players, just noting what can be done in the draft, as far as players go...