Tragic may be an overstatement. He could be back to 100% a couple months from now depending on how fast he heals up. You can't call it a career for a guy just based on getting his knee scoped. This really hurts OKC's seeding this season though, I think. I see them moving back from #1 to #3 in the standings at the end of the season.
If Westbrook misses the first 4-6 weeks of the season I'd be surprised if they made it to #3 seed in the West. I've got them #4 or #5. 1-3: Spurs, Clippers, Rockets 4-6: Grizzlies, Thunder, Golden State