I really think they slammed their window shut by getting rid of James Harden.
Or, rather, how they dealt with the whole Harden issue in general. It's one thing that they let Harden go, but they did a terrible job trying to fill the void left by him, and now are in salary cap limbo.
Even when Westbrook comes back, he may be limited for the rest of the season. Perkins and Sefalosha are basically non-factors at this point, except in specific match-ups. Reggie Jackson and Jeremy Lamb have yet to show more than occasional flashes of competency. Ibaka is good, but he needs to take another leap.
Unless Ibaka makes a leap, or Durant takes things to another level, they need a serious shake-up to be real contenders again. Scott Brooks is borderline worthless as a coach, and their GM is extremely overrated (he got lucky on a couple of draft picks, but has done a terrible job managing the team salary-wise).