Brady leaving New England was just a fraction of the problems the Patriots had that effected their poor play this last season.
BB hocked the next few years to win a couple of more rings. Brady did help by not demanding a larger part of their cap but it was a lot more than that.
BB missed on a few draft picks no doubt but he didn't forget how to coach.
The only reason he signed Newton was he signed super cheap. It was a last resort.