I assume Duke will see the same type of transition other schools have when an all time great retires. UCLA dropped from dominant to very good. Gene Bartow actually had a better winning % than Wooden (85% vs 81%) but he was run out of town for not being Wooden. When Dean Smith left UNC, Guthridge took over a great roster and did well for one year, then the plunge to mediocrity set in. After the talent was gone, Gut retired and the debacle that is Matt Doherty came in and destroyed all remnants coach Smith.
When K retires, I assume he'll leave a stocked roster with lots of talent. Whoever takes over will do pretty well for a couple of years, but I expect a step down from K's success. By year three or four, the successor will be run out of Durham for not maintaining the level of success the fans are used to. Will be interesting to see who gets the job as sacrificial lamb and who is the second guy (more likely to get a fair shake)