Vanderbilt, Richards, Green, and Washington are all potential OAD guys.
No!
Green is probably too small to be a OAD, your smaller more distributor than scorer PGs don't often go after 1 year. I can't think of any in recent memory.
Washington is also a bit undersized for his position, PF, an probably needs to improve his perimeter game & quickness to be a SF. So he too is very unlikely a OAD, unless he breaks out like the Mich St player did this year (unlikely, as we will have more balance).
Richards, could be OAD, but only if Bamba doesn't come. I would think Richards would need to see the court at least 18-20 mpg to consider leaving after 1 year.
Vanderbilt or Gabriel (but not both) are the most likely candidates. If one of them shines above the other, then I think he would leave.
The 2018-19 roster is likely to look something like this: Richards, Wynyard, SKJ, Gabriel or Vanderbilt, Washington, SGA, Baker, Green, + FR. That is 8 returning players, & thus
5 FR openings. Ideally I'd like a couple top players (like Williamson), 1-2 other top 20-30 players, and one or two 40-100 players.