LANDOVER, Md. — The Dallas Cowboys season ended just how it started with the fate of coach Mike McCarthy and the legacy of quarterback Dak Prescott left to determined by what they do in the postseason. Moments after the Cowboys beat Washington Commanders 38-10 to secure the NFC East title on Sunday, owner Jerry Jones spoke about the team’s successful regular season and the coach that led them to the No. 2 seed in the playoffs. It marked the third straight 12-5 season for McCarthy, who became the first coach in Cowboys history win 12 games in three straight seasons. In the same breath that Jone…