I understood the problem with him is that he doesn't want to play basketball in the NBA anymore. If that is the case a new team isn't going to change anything. If he changes his mind and decides he really does want to play, why would he want to play on the Celtics over say Cleveland? CLE seems perfect for him, smaller market (he doesn't seem like the Miami, LA, NYC type), but great team in terms of winning potential.
So they are just going to buy him out? No going through waivers to see if someone else will take him? That tells me he doesn't want to play anywhere.