1. If he's projected to be drafted in the first round, or even high in the 2nd round, he's gone to the NBA. He'll take whatever signing bonus he can get and do his best to make a roster.
2. If he's projected to be drafted late in the 2nd round, or undrafted, he may opt to return to BYU, but I think that is unlikely. I think it's more likely that he tries to latch onto an NBA team as an undrafted free agent and try to make a roster. If unsuccessful, he can still go to Europe and make a very good living there.
Here's my reasoning why it's most likely he's gone:
1. Although he's not old, he's older than a lot of talented players are when they enter the draft. The clock is ticking.
2. He's married, and is anxious to get on with his life and start making a living to support his family. Having served a mission in Italy also makes the idea of Europe (especially if it's Italy) more palatable.
3. Given the current state of the BYU program, he doesn't see that staying another year will improve or change his current options much.
One thing that MIGHT persuade him to stay if his projected draft status isn't good: BYU makes some changes to their coaching staff and brings on someone who is known to be very good at coaching and developing bigs. I wouldn't hold my breath on this.