I did a study a decade ago, (when people wanted JB fired), in which studied what happened after the top 25 winnigest major college football and basketball coaches retired, (or got fired or died). 84% of the time his successor had a lower winning percentage. The key is to be the next guy after that.
Even great programs don't go from one Hall of Famer to another. UCLA has had 10 coaches scine John Wooden retired in 1975. The one with the most wins is Ben Howland. North Carolina didn't go from dean Smith to Roy Williams. kentucky didn't go directly from Rick Pitino to John Calipari. there are exceptions: Louisville went from Denny Crum to Pitino and Kansas went from Williams to Bill Self. They had the courage to bring in a guy who had been a successful head coach elsewhere.
In my study, new coaches with prior experience as head coaches replaced 'legends' with an average winning percentage of .714 and had a winning percentage of their own of .665. Coaches with no previous head coaching experience replaced legends with a .710 winning percentage and had a .573 percentage of their own.
Still, I'll be shocked if JB's successor isn't a current member of the staff. if that doesn't work out, then we'll look elsewhere.