If Manning is relieved of his duties now, Wellman can say with a straight face that this was a successful transition from the Bzzzz years, which Wellman of course created. In 4 years, Manning would have taken the team back to the NCAA tournament, greatly increased the level of recruiting, and successfully signed a top-15 class coming in next year. The new coach can look forward to inheriting a roster with a lot of potential, and future facility upgrades as a serious chip on the recruiting trail.
When to let a coach go is very simple. When your goal is to compete for conference championships, and deep runs into the NCAA tournament, and you know the person who you pay $ millions each year is not a good enough coach to get it done, it is time to move on. Manning is one of the three worst coaches in the ACC, and we're not going to succeed hoping to out-recruit UNC and Duke. That thought is laughable.
ETA: We will lose on Tuesday, and Manning will be back next season. I'll be absolutely shocked if he's not.