I have less concern over whether or not Roy can produce than I do that he can stay healthy for a full season. He has only played 16 games once and that was 2006 when he went to the Pro-Bowl.
Frankly, we don't need him to catch 100 passes for 1500 yards and I seriously doubt he will. I would rather see him as just one of the weapons we have on offense and see the ball spread around a lot more than it was last season.
With Roy, Witten, Bennett, Felix Jones, Barber, Austin (I hope), Crayton, etc. all being part of the passing game, we should see the ball distributed much more evenly than last year.
Williams doesn't need to be THE GUY, he just needs to be reliable and make plays when his number is called.