A hobbled Ibaka that has rushed back from a calf injury is not going to let the Thunder win 4 out of the next 5. So far, these two teams have played 96 minutes. The Thunder have been competitive for about 30 minutes (not superior, just competitive) and have looked laughably outclassed the other ~66. Ibaka is good, but the Spurs are out-executing the Thunder all over the court, and one power forward isn't going to solve all those problems, especially if he isn't 100%. That even goes for some of the paint defense problems.
Even if Ibaka somehow comes back 100%, I don't see it mattering. The Thunder only barely came back from the 0-2 deficit in 2012 and if not for a cold-blooded performance from Harden in game 5 or some questionable reffing in game 6, that series would have gone to game 7 in SA (i.e. advantage still to the Spurs). This is a much different scenario, even with Ibaka. The Spurs are much, much better on defense than they were in '12 (that unit was above average, but nothing special whereas this Spurs team has an elite D in the top 3-5 range), and they're a decent bit better offensively too. Even with a healthy Ibaka, I think each game is at best a 50/50 proposition for the Thunder, and probably worse.
To me, this series hasn't just highlighted how much the Thunder miss Ibaka, it's also highlighted the differences in systems and approach, and some of the major deficiencies that the Thunder have. Specifically, they need to run a freaking offense; it's not a team of 20 year olds anymore. The solutions, as Durant and Westbrook said over and over in the postgame conf, aren't "play even harder" or "fly around more" or "we've got to contest." The Thunder need to study the film to make improvements on D and run some actual plays on O. Nobody on the Spurs cares that Westbrook is twice as fast as they are in a footrace. They're content with knowing that their passes are faster than Westbrook and that they can bait him into dumb decisions on both sides of the court.