As much as I like Nash, wouldn't do the trade even if it included Baby in a S&T to get Gortat. It's frustrating to watch Rondo's inability to make jumpshots, but I don't think that was the main reason why the Celtics lost.
I bet they missed TA more than Rondo's jumpshot, who's never been around, and the biggest hole in the Celtics roster was the lack of defensive big bodies. Kendrick was missed, but also was Sheed, and PJ Brown. JO played better than Perk last season, and even Semih looked good. But in the playoffs the lack of Shaq was crucial.
So the Celtics should target Howard to adress the inside flaws, and if they can't get him, another real big like Marc Gasol or Bogut. The idea of getting Chris Paul sounds great, and he'd be the only PG I'd trade Rondo for, but his knees are kind of scary.
I think the Celtics should try to get OJ Mayo, who was projected as the best of his class and is a great offensive player, and wants to play with Rondo. Rondo, Mayo and Green seem like a good start to build (with Avery, JaJuan and probably the Big 3 in lesser roles that would be a great roster next year). I also would like them to undo the Semih to Cleveland trade, leaving Gody in Ohio so the Cavs end winning the trade.
Next summer, if they can attract Howard, great. If not, they can still use the expiring JO contract and some youngins to get a decent Center for the future.
You can't expect Nash to play this good (even without D) for a long time, so I wouldn't take that gamble.