Personally I think McCullough is the most likely to go. Don't know any inside info but it's known if you read the board that he has thought all along he was a one-and-done.
Gbinije should definitely come back. He got hot for a stretch but he's not ready for the NBA - not by a long shot. And unless he really hates college that much, which as a basketball player at a Division I institution I'm not sure how that's possible, he will stay.
The two other guys would be kind of crazy to leave, unless they're told they won't play many minutes next year by the coaching staff. I would say Patterson would be the most likely to be given that ultimatum, with Richardson coming in with accolades to go along with Joseph, Cooney & Gbinije all coming back.
I have never been as big a BJ Johnson fan as many on this board, but I still think he could add some value as a shooter at this level. He really needs to improve in the strength department, however, if he's ever going to play on the wing in our zone. You have Roberson, McCullough (maybe), Gbinije (if he's back, and if Joseph/Cooney remain starters which they probably will), and then a bunch of unknowns. I really think Lydon is going to impress people - but there likely won't be many minutes to go around.