A much more interesting conversation might start with the question: What if Tom Osborne continued to coach another 5 years instead of 'retire' to become a Congressman and Governor wannabee? My answer: we'd have won atleast 3 more national titles and maybe wouild have then hired a truly great coach to replace him instead of Frank.
The Nebraska job, following TO, would have been a daunting one for almost any rising young star type as it would have been almost impossible to continue at that highest level possible. But, a great coach would have done extremely well. Frank did 'OK' until he ran out of great players and then fired a bunch of excellent coaches and replaced them with guys like Craig Bohl, etal. Bo Pelini was a darn good hire but would never had stayed as Frank's Def Coordinator long and was not a Head Coach in too many ways, personality wise. He may have known more than enough about defense and some offense, but he was not CEO enough to run such a high profile program.
Recruiting was Frank's glaring failure and it is well known by most who watched the program closely. Many casual fans were simply unaware of the serious lapses in this area. Without talent, you are not going to win championships (conference playoffs, bowls, or national titles).
The biggest mystery to me is simply Why did Tom retire and name Frank his successor? They were close friends certainly but Tom was close with many of his assistants, quite a few of which would have been superior choices over Frank.