Dez isn't going to have same type of impact without Romo. Not the way he is used in this offense. This isn't not a knock on Dak or Dez . If you watch the All-22, it's very evident.
Dez is mainly asked to run routes that take long time to develop. Romo would hold on to the ball until Dez gets open, Dak mostly doesn't. He'll look at him and if Dez isn't open he goes to the next read instead of waiting for Dez to get open. I think that's what he is coached to do.
Another thing is, Dak isn't good at throwing the fade near the endzone. Not yet anyways. With Romo, it's almost automatic TD.
Unless the coaches change how Dez is used, he will not have the stats he used to get with Romo.