Ainge probably will buy out Prince, because he's been a good soldier since he's gotten here for what was always assumed to be a short stay. I'm sure they've already talked about it, and will again if no trade happens. If Prince isn't bought out, it will be because Stevens convinced both Tayshaun and Danny to have him remain on the team.
I don't see either Bass or Thornton going. Bass has been here for awhile, doesn't seem to be clamoring for a buyout, and is a candidate for a Humphries-like sign-and-trade next summer. Thornton also seems to be fine hanging around. He gets his minutes, and gets to show other teams he can be a veteran leader, which will help him transition to a different phase of his career. In general, Ainge is very anti-buyout, because it lets other teams get his players without giving up assets for them.