Dallas could get by this season by just trading Estes, a very good and young RB. No impact on the cap. However, Estes is worth no less than a no. 1 draft choice, or a cheaper quality player together with a high draft choice. With Estes gone and $2.3M in cap space, Dallas can sign a dozen or so players for the remainder of the season at minimum salary.
Trading young WR Barnett could also provide more flexibility w/o adversely impacting the salary cap.
Trading Dallas' other better players who are signed long term will impact the long-term cap negatively because of the contracts signed.