Sheed retires and the Celtics re-sign Perk.
Why would Sheed leave all that money on the table. I think you should plan on him taking his player option, the Celtics certainly have to. Perk has two years left on his deal, we'll need to sign him or another center. Big men make a lot of money the Celtics have to plan to pay him or an equivalent player.
Again I don't see Pierce leaving 21 millon on the table, I also don't see the Celtics extending him at 14 million for 4 years. I think you're being overly optimistic on a lot of things.
I don't think the Celtics will keep their payroll around 85 million, not unless they're actually winning a banner each year. Taking on Stephen Jackson will mean Ray or Rondo is gone, to do otherwise would tie this franchises hands for the next 3 years.