There is no way Adam Silver makes such a strong statement that he did today if he does not have the votes/backing of the other NBA owners
They other owners may have but Sterling could drag this on out of spite. He still owns the Clippers where the owners could remove the team out of the league by banishing the them. They, the NBA, can’t sell the team for Sterling.
He may have the votes, but the NBA Constitution does not address this type of private behavior. Adam Silver is going to lose in the end.