I'm not sure that our lack of 20+ yard completions means that "we rely on the running game to score" though. When we convert on a 3rd-down pass, our average to-go distance is 6.13 yards, which is in the middle of the league (16th), so our running game hasn't especially helped us convert by the pass. And those conversions extend drives that eventually end in touchdowns. Our of 15 TD so far, 10 were scored on drives that were kept alive by a 3rd- or 4th-down pass.
And we lead the league in conversion percentage on 3rd- or 4th-down passes. (If Dak had Andy Dalton's conversion rate, for example, our offense with its improved OL and RB would have 5 fewer touchdowns.) Of course we may be leading the league in conversions with Romo as well, but that's no less speculative than whether Dak can maintain his current pace.
And I don't think Prescott's 52% red zone completion percentage is even noteworthy. Rodgers, Rivers, Palmer, Carr, and Wentz average 7 TD (rushing or passing) 0 INT and range from 47.6 to 54.5% completions in the red zone. Dak has 6 TD (rushing or passing) 0 INT in the red zone.
Where I do agree is on your last point. We know the 2014 Romo was outstanding against great defenses. If he comes back and can be that guy again, he's the best option, and gives us the best chance in the postseason. Also things that remain to be seen.