Here are the "bench" players that played in the playoffs this year. Each one played in at least 11 of the 19 games broken down by potential roles (I've added Theis who was hurt).
Main rotation - Rozier, Smart, Morris, Baynes, Theis
Deeper Rotation - Ojeleye, Monroe
Suits - Larkin, Yabu, Nader
That is all 15 players when you add in the 5 "starters" in Irving, Brown, Hayward, Tatum, and Horford.
Of those 10 bench players, I'd be surprised if at least 5 don't return, such that I'd expect 5 or fewer to actually be back.