I think in the Cowboys case, they do need to start over, starting with a new GM who hires the coach. For the last 30 years, it's been Jerry year after year believing the Cowboys are SB contenders and forcing his new hires to try and make these delusions work. But I get what you're saying. Even Jimmy Johnson didn't go wholesale, he kept quite a few Landry pieces.
Look I just look at the other teams that have had more recent playoff success. They've all have had the benefit of a down period and a chance to retool with higher draft picks. And while you are loading up with higher potential talent, then you have the salary cap space to be more aggressive in FA and spend more. That's how I see it.