Koll will be there until he retires. By that time he will have his predecessor already in place and UNC will be right in the thick of Tier 1 in the ACC (or B1G if they are there then - which I think they will be... which means Tier 2 there behind Penn State).
Terry just hasn't run a top tier program as the CEO like Tom does and has been doing. He left the UTC job to be Tom's assistant at VTech. He has been the primary guy to focus on development, but he has never been a CEO like Tom, Koll, or Cael (BLESSED BE HIM AND ALL THAT IS HIS).
I fully believe if he gets a smaller program (I am thinking a smaller B1G, B12, or ACC) he would vastly improve it very quickly. Recruits would follow to be with him and in his first class to be 'those guys' that changed the program.