I think predicting a top 4 finish next year is a little much. Is a 3rd or 4th place finish possible? Without looking at what the other teams are losing and bringing in, I'd say maybe.
And something to keep in mind on M'Baye. Unless he can play the 3, and LK will play him there, if he is putting up 15 points per game, that means Osby or Fitz is averaging less as well. Meaning, we're getting pretty good production out of our starting 4 and 5. Where we really need better production is from the guard spots. So unless M'Baye starts at the 3, we aren't simply adding 15 ppg to our lineup, if that makes sense. If M'Baye were a true guard of the same talent level, I'd be a lot more optimistic about next season.