I don't know where all the Belichick to Dallas stuff started at but it was a complete never-gonna-happen for me. Since Jerrah and Jimmy parted ways, Jerrah's hired seven coaches - six of them were Jerrah yes-men (Switzer, Gailey, Campo, Phillips, Garrett and McCarthy) - with Parcells the only outlier.
Parcells did the Lord's work getting that Quincy Carter 2003 team to 10-6 and the playoffs but didn't win a game, then had a transition year, then went 9-7 twice w/the only playoff appearance the infamous Romo fumbled snap game, so with that level of "just okay," I think the die was cast for Jerrah sticking with "his guys" as coach. Jerrah also likes coaches who have success but also let him play Dr. Jerrah team medical spokesman and go on his radio show etc. and Belichick was never going to stand for that (neither were Harbaugh or Vrabel or any of the other "name" guys).
McCarthy wins a lot in the regular season (which does have value) and Jerrah doesn't care about winning another Super Bowl (he has three), despite what people tell you. He cares about the Cowboys brand and being #1 on the Forbes list and from that standpoint, things have never been better.
I will go on the record (I sort of did earlier in this thread) and say that the next Cowboys coach after McCarthy is Deion Sanders. He's a bigger name than the Jerrah yes-men hires were but will be beholden to him for giving him a chance at the NFL level and they have a great relationship.