I think that if he gets a first round promise he comes out. At least he's guaranteed $$$, even at the very end of the first.
If no promise, despite what I've been thinking all along that he will definitely come out, I think that Giles gambles and stays in school.
If he opts to come out and gets picked 2nd round, he's guaranteed nothing and has to fight for a spot on team. If he ever gets injured in that scenario, fighting for a spot on a team and a contract, he's done value-wise.
If he returns to Duke, he gets an education, and if he's lucky, continues to get stronger and proves himself next year with lottery position. Of course, if he gets hurt again, he's cooked.
It's a gamble, either way.
Personally I think he comes out with a promise from a playoff team with some talent already that they can take a chance on him. San Antonio and Toronto come to mind. Utah has two late firsts, including #30. They could be in play too.
I guess that there is one other scenario. If he declares and is not taken until the second round, maybe he can get a pro contract overseas. I don't know how that works though. (guaranteed$$$, length, etc)