Three years from no,w with Rondo and Pierce being the only ones on the books, if Danny is careful about how he handles the rest of the team salary, he will still have a bunch of flexibility to add at least one max level free agent.
Remember, after the new CBA kicks in max salaries are probably going to be smaller per year and salaries as a whole will be lower. Also, if the economy turns around and the league prospers, the salary cap might be higher. Also, if Pierce is adament about actually playing that final year and he is a hindrance to this team, then the C's can hardball him and tell him to either except a very, very favorable buyout of his contract or he can go end his career elsewhere because they are going to trade his expiring contract.
This fourth year guaranteed means very little to me. First, the team is going to save over $12 million next year alone. Then, is the lockout is extensive the Celtics will be not paying anyone during the 2011-12 season. At this point it looks like the owners are going to be getting the TV money paid to them during the lockout so the C's won't be losing a fortune during the lockout.
So there's still an eternity before that year comes and anything could happen.