He should get an evaluation by the NBA undergrad advisory committee this year and see if he gets an invite to the combine. If he gets a committe first round grade, he should declare. If he gets a second round/undrafted grade and doesn't get a combine invite, it would still be good experience for him to go through team workouts. The longer he waits, the more his draft stock is likely to fall. A lot of good seniors end up in the second round, and many never get drafted at all.