Both Pierce and KG have earned enough money by now. And really, that's why they were traded because of high salaries, respective to their ages.
They can both get bought out by their current contracts and joined the Celts for Vet's minimum. And now that Rivers isn't coach, Stevens can actually play 'em off the bench, 5-10 mins per game max when the game slows down, and it's a half-court style of play. During run 'n gun plays, they sit, as older players are less effective in those scenarios.