i would advise him to declare and go thru the process but definitely with an eye on returning unless he dominates the workouts and camps and shoots up people's boards
I honestly dont know what the new rule is today, but back in 2004-2006. If you entered the draft, were not drafted and did not hire an agent you could return to school.
You can't do either of these things today. The NCAA purposely made the declaration period earlier than the dates pro staff are allowed to even talk to the players. Before the NCAA's deadline for withdrawing. I liked the old way better too.