I bet he will come out. Going back to play against inferior talent for a whole year won't help him as much as getting in an NBA strength and conditioning program.
To me, Marcus Smart is a cautionary tale against going back, even though he will still go top 8. He went back, played a little better, and still got eliminated because his team couldn't give him any support. If you're a top 3 consensus pick, you are set for life with just your first contract. Get that money and improve your game at the highest level.