I think it was inevitable that one of the 4 wasn't coming back. I don't think it is that far fetched that those 3 return. Oleg was always a project. And he's not going to end up transferring anywhere at a major level right now. Walker is a senior next year and Keita a junior so there's definitely a window/path towards future playing time, even if it doesn't happen now.
Not to mention, that while, it might not be ideal or prototypical for Fred's system, but Walker can give us minutes at the 4 as well, opening up time for Oleg to back up Keita. You need 4 bigs to have a chance and right now that's what we have provided we don't add anyone this offseason.