I think Bill could have gotten the Dallas job. I really do. Would he need to let go of some control? Sure, but he was willing to do that here anyway and he needs to know no one else will let him have the control Kraft did anymore with the questions on his ability as GM and how he has managed every non Brady offense.
it seems the Cowboys waited a while to announce they were sticking with McCarthy, as if they were waiting to see if they could get someone they really like instead of a holding pattern. Which is exactly what I think happened. They wanted to move on but for a guy they were confident could help them. Maybe like Bill or Haubaugh or some really hot up and comer.
Personally I don't think Bill wanted the job. If Bill takes that job he HAS to produce or his legacy takes even more of a hit. Imagine if he lands on one of the more talented teams with a good QB, and all they need to do is play up to their ability, but Bill can't make them do it (or worse, they regress). Bill might poo poo stats, but in reality he's very big on legacy and perception. If he messes up in Dallas on a huge stage with a good team, he will never be brought into the GOAT discussion again.
If however he fails in Atlanta well, there may have been some potential but weren't all that good and Ryan outside of a few years hasn't been impressive. Also not a big market so people wont be watching as closely. And if Atlanta improves he gets all the credit. Its a no lose situation.