Again - you can exceed the salary cap - it's not a hard cap. I can see OKC winning at least 1 title in the next 3 seasons, counting this one - selling out every home game - plus all the merchandise and stuff like that - they are going to be in a financial position to keep that team together despite likely having to pay some luxury taxes.
Boston's payroll this year is ~80M.
Harden and Ibaka - along with Westbrook, Perkins, Collison, and Durant - are all under contract for next season and the season after that (so is Eric Maynor, a really solid PG who was hurt all season). Harden and Ibaka are still under their first contracts, so OKC can extend them or re-sign them to longer-term deals. Under the new CBA, they aren't immediately eligible for max-contracts. Harden was picked much higher in the draft than Ibaka was, so his base is much higher.
Even if Ibaka and Harden WANT to leave OKC, they can't do so, on their own, until the 2014/2015 season.
Also - Hibbert is a better offensive player than Chandler, but he's restricted, I can't see Indy letting him go, even with a front-loaded contract.
As for Deron Williams - he'd be a nice fit in Dallas, but I'm still not sold on a core of Deron/Dirk/Marion/B.Haywood.
the other good 'young' team I left out is Memphis btw...