You do keep the OBC. If you are bidding on Retreat I would email Celebrity to see if they include dinks. I say this because the rule is you don't get any promotions associated with the new room but you do get the standard benefits of the room class, not sure if drinks are considered a promotion or part of the room for retreat. If you are bidding on Aqua you don't get drinks.
FYI, the same thing happened to me, within the 90 days they charge more than the difference between cabin prices. Leaves Move-Up as the only answer.