The safest answer is "too early to tell," and Serge Ibaka is a large reason for why the guesswork is just that. As Zach Lowe of Grantland puts it, Serge Ibaka is now the "most important player in the NBA."
"Most important" is different from "best," and Ibaka's importance hinges on the wide chasm between "ceiling" and "floor," combined with Oklahoma's specific place as a spitting-distance contender for years to come.
Serge can shore up a shaky Oklahoma City defensive frontcourt. He hasn't exactly done so thus far, but at 3.7 blocks in only 27 minutes of play, Serge flaunts a skill set from which greatness can arise. The young big man has incredible potential, but he's yet to demonstrate to harness it.
Ibaka's improvement will determine whether Oklahoma City can survive this decision. Ranked ninth in the league in defensive efficiency as a team, it will be exceedingly difficult to make it back to the finals, sans improvement on defense. If they're losing considerable offensive productivity from James Harden's departure, it must be made back on the other end.
Last year's finals showed two kinds of Serge Ibaka, good and bad. First, here's the bad example. Chris Bosh pump-fakes Kendrick Perkins into another dimension and drives to the hoop. Serge should come over and contest, but he falls asleep on defense.
Earlier in the game, though, Ibaka showed what he was capable of in a similar situation. Chris Bosh pump-faked Perkins out of the way, and Serge flew in like a vulture.
Serge Ibaka can become Oklahoma City's response to Dwight Howard, and save them from bridesmaid status. He also possesses the added bonus of offensive competence. Ibaka is the rare shot-blocker who can hit 18 footers with regularity. With Harden gone, his ability to space the floor will be a massive help.
Russell Westbrook also needs to take a step forward, so as to help the Thunder keep pace. Westbrook has improved markedly as a shooter, but his decision making still leaves much to be desired. James Harden was the de facto point guard for many Thunder possessions, and it's incumbent on Westbrook to become more of a distributor next season.
Kevin Martin will help OKC, but his future role with the team remains unclear. He's on an expiring contract, and it's anyone's guess as to whether he'll be back next season. In his possible absence, Oklahoma City has some cap space to toy with. Unfortunately, based on how they've dealt James Harden, I'm pessimistic as to whether the Thunder will use this money to actually get better.
That's the most dismaying aspect of this Thunder move. Much as they might tout "flexibility," this was a money move, on top of everything. If a team chooses cash over a better title chance, I'm not going to fulminate over it. But, if I'm handicapping their future chances, such a move is worrisome.