No agent? I think if he's not going to get drafted he won't go, but it sounds like he'd go even for a second-round pick and a shot at making a team. Keeping his options open.
Why won't he come back? I think the chance of getting injured at BYU is greater than the chance of another year in college showing NBA scouts anything they haven't already seen.
I personally think he is looking for any reason not to come back at this point.