Down 0-2 with no Ibaka: Hopeless, it would take a miracle
Down 0-2 with Ibaka: The deficit suddenly doesn't look like a big deal. Win 2 home games against a team you matchup well against and the series is back on.
Ibaka is a good part of OKC does so him coming back should help. But I don't think his absence is the only reason the Spurs are absolutely destroying OKC. If Ibaka Flocka Flame comes back and OKC somehow wins this series, Durant should just give his MVP trophy to Ibaka.