It goes without saying that Zendaya (Rue) will be back for "Euphoria" season three. Beyond that, Sweeney, Dominic Fike (Elliot), and Eric Dane (Cal) have both confirmed they'll be returning for the new season.
Barring any surprises, the rest of the main "Euphoria" cast members will probably return for season three as well, including Apatow (Lexi), Hunter Schafer (Jules), Nika King (Rue's mum, Leslie), Alexa Demie (Maddy), Jacob Elordi (Nate), Storm Reid (Gia), and Colman Domingo (Ali).
Javon Walton probably won't return following Ashtray's apparent death amid the shoot-out (barring any surprise twist that sees his life saved, of course). And sadly, Barbie Ferreira (Kat) confirmed she won't appear in season three. Cloud is also very unlikely to appear in the new season unless old footage is used.