Smart seems like a good guy. He doesn't seem like the type that's going to speak negatively of a teammate (yes Kyrie is still technically a Celtic.)
It seems there's 2 different paths the Celts could take this summer:
Path 1 is the Celts keep Kyrie and attempt to lure in a big fish to play alongside him. Obviously AD is the first name that comes to mind though perhaps there might be some other options I can't think of. In this scenario, I think 2 of Hayward, Brown and Tatum are gone. So the team will basically revolve around Kyrie, insert star player, Smart and Horford.
Path 2 is Kyrie leaves and the core of the Celts is Smart, Tatum, Brown, Hayward and Horford. However, they still possibly ship at least one player in a trade for a big, so we'll still be competitive regardless because I don't think anyone has the time and energy to take a step back and go through another rebuild.
Either way, I think (and HOPE) we'll be much better next year and will have learned from this past season.