Frankly, the responsible decision is to leave for the NBA now. He has a family and that should come first. There's no guarantee that his draft stock will ever get higher than it is now (see Craig Brackens), and while I'd selfishly love to cheer for him another year, this kid deserves some success and I'll wish him the best of luck on whatever he has decided. Even more importantly, how awful would it be if he suffers a serious injury next year in an Iowa State uniform.
Finally, I think it's probably important that Fred directs him to the NBA. We want Fred to be seen as a coach who cares and can get his players into the NBA in an effort to start to recruit some of the top level talent. It's an investment in our recruiting future. If Royce stays (all indicators point elsewhere), I would hope to hear that it was his decision to stay and that his coach had told him to go to the NBA.
Good luck Royce, I may actually start watching the NBA when you get drafted!