Since he increased his cumulative 3-point attempts from 22 to 51 in 2012-13, asking him to completely eliminate that shot is not realistic. Realistic is he'll probably shoot about 80 of them in 2013-14.
It doesn't take much for him to elevate from "slightly above 5-of-20" (Harney was 12-51 last season, for 23.5%) to "slightly below 7-of 20". When he takes a 3-pointer, he's typically wide open with his feet set...he never shoots a 3 on the run, or with a hand in his face. He just needs to drain those open looks.
And an additional barometer for the 2013-14 season - Diggs time spent at PG*. If he's rarely at the point, we'll be in great shape. If he's logging 8+ mpg at the point, we have problems.
*Preempting Zipmeister - this is assuming Diggs plays for the Zips next season.