It's hard to say Duke won't miss a beat without Tyus. And that's not a knock on Derryck. But Tyus was pretty damn special. Considering he was a freshman just makes what he did all that more impressive. Tyus kind of had a switch, and mentally he's one of the toughest PG's Duke has ever had. That's saying something.
I also hope comparisons of Thornton to Jones are few and far between. Derryck is his own kind of special player and we're all going to love him.
In terms of aggregate production over a 40 minute game, I actually don't think there will be much of a drop off at all from Tyus to DT. As great as Tyus played, his aggregate numbers weren't overwhelming in view of his usage rate -- averaged 11.8 ppg and 5.6 assists on 42% shooting, and 38% from 3. QCook's numbers as a soph. PG were actually pretty comparable -- though obviously I think Tyus had better advanced medtrics. And, from what I've read, DT will be an upgrade defensively.
With that said, no doubt that we're going to miss Tyus's poise under pressure in the last 10 minutes for games -- where, he not only seemed to always play his best basketball, but often was borderline unstoppable. While Duke's had other great players who played well under pressure, aside from Laettner, not sure I can remember a star player who was as consistently reliable in the biggest moments as Tyus -- including many players who I think were clearly better than him. For instance, even though I don't think Tyus was nearly as a good as a soph. or jr. J-Will, not sure I wouldn't take Tyus over him in any final possession situation. I really think that is what we will miss most about him -- as we don't have any established stars returning, and its impossible to know how the new guys will perform in those kind of moments. As much as people reflexively say the 13-14 was a fundamentally flawed team b/c of size, PG play, etc., the biggest problem with that squad was it regularly lost the last 3-4 minutes of games b/c our star players (Parker, Hood) seemed to get tight and the team as a whole tended to not play well. That's where I think we're really going to miss Tyus.