Instead of looking back at the trade deadline, let's look ahead at some teams the Celtics could trade with in the summer. Most of the ideas involve the Celtics embracing a long-term rebuilding strategy by renting cap space for assets. The model involves doing what the Cavs have done in absorbing contracts such as Baron Davis and Luke Walton for first round picks.
Atlanta Hawks
Josh Smith wants out. He has one more season for $13.2m. Trading Smith to a team with cap space for draft picks would generate a trade exception that they could use to grab a replacement, but they have little in the way of trade assets and an exception won't really let them get much farther over the cap.
Chicago Bulls
The Bulls are a bit tax-phobic, from what I understand. They have Omer Asik, a restricted free agent if they give him a qualifying offer whose maximum possible salary is capped at the league average. They have $10.5m tied up in Kyle Korver, Ronnie Brewer, and CJ Watson, but only 500K of that is fully guaranteed if they players are waived before an appropriate date. Even if they waived all three, they would still be over the cap. A team with cap space could give them a trade exception by taking on the salary of Richard Hamilton ($5m for next season, only $1m fully guaranteed the season after that). A second round pick for Hamilton and either Jimmy Butler or a future first-rounder might be fair.
Dallas Mavericks
With Dwight Howard off the market, the Mavs may still be chasing Deron Williams, but they still need to shed some salary to create cap space. They might be able to clear enough space just by waiving Odom before his contract becomes guaranteed and using the amnesty clause on Shawn Marion or Brendan Haywood. Dominique Jones and Roddy Beaubois are the young players who could be added to a deal with or in addition to draft picks.
Golden State Warriors
I have no idea, but the Warriors have always been prone to doing things that don't make sense. They would probably be willing to deal perfectly useful players to clear cap space to make a bad free agent signing.
Los Angeles Clippers
The Clippers could be willing to cough up something in order to get rid of Mo Williams and his $8.5m player option and/or the $4m owed Ryan Gomes (he's still a Clipper, right?)
Memphis Grizzlies
The Grizz may want to keep OJ Mayo and give away a player like Dante Cunningham (or even Quincy Pondexter) for a second round pick. They may also make a choice between Darrell Arthur and Marreese Speights and be willing to facilitate a sign-and-trade. The reason a team with cap space might deal for either is because both could be restricted free agents and the Celtics may want to give away a future draft pick to avoid having to over-pay on an offer sheet.
Orlando Magic
With Dwight Howard back for at least one more year, the Magic would love to find a way to bring in a good player to team with him. While I would rather just try to sign restricted free agent Ryan Anderson away from them, one might also be able to trade a second round pick for Hedo Turkoglu, JJ Redick (who can probably be flipped for a younger player or a draft pick later), and at least one first round pick. That would give the Magic an approximately $18m trade exception, though it would also leave them with less assets to use with that exception in a trade.
Sacramento Kings
Kind of like Golden State in that I'm not sure what they have to offer, but you have to be prepared to take advantage if they decide to do something stupid.
Cap space has value beyond just free agency. If you think the Celtics should embrace missing the playoffs for a couple of years in order to rebuild, these are the kind of trades you should be interested in making.
Personally, I would rather try to reload by bringing back KG and trying to get Ryan Anderson or some other plan. But if I didn't, this is how I would rent out cap space. You might have a tanking team with a starting lineup of Rondo, Rip Hamilton, Pierce, JuJuan Johnson, and Greg Stiemsma, with a bench of Hedo Turkoglu as a combo forward, JJ Redick, Avery Bradley, and a bunch of rookies (I like Yancy Gates if he remains projected as a second rounder), D-League All-Stars, and journeyman bigs because you there are few of those in the D-League. If Rondo or Pierce suffers an injury that lets him credibly miss 30-40 games, that could be a high draft pick.