I'd call it the reverse Chris Paul effect. We were told CP3 had to go because of the the endorsement money that was on the table (who knew State Farm would build a series of commercials around him).
John Collins is the unknown star, that leaving this year would get a 1st round contract, but likely zero endorsement money.
The upside of staying, he could be pre-season ACC POY, 1st team pre season AA, on the Wooden list. His team would be pre-season top 20. He knows he has Brown coming in that will make the team better, so he doesn't have to carry the team enabling Wake to be an ACCT contender and a Final 8 or better quality team. Wake would go from ESPN3 obscurity to national games with dook (note we didn't even get national TV with dook in 2 games this year) and UNC, where he would be showcased. After all of that he'd be a known commodity and could enter the NBA with endorsement contracts in his pocket.
What's the down side? Sure he could have a serious injury, but anyone of us could also be dead tomorrow. The other worry is that his game is overly scrutinized and he drops in the draft. His offensive game is solid and very developed, he's not a guard with 45% 3pt shooting that is at risk of having a bad shooting year. The core of his game is not going away. Given his level of improvement I'm guessing he would be able to improve his defense and he outside shooting (or at least extend his range).
Right now he's like a AFT, Teague or JJ. Can go to the first round but will be there in anonymity, stay and he can propel himself to the national spotlight and enter the NBA with much more hype.
I'd say that it the argument that could be made for staying.