The contract under which Sterling obtained his ownership interest is 33 years old. It's doubtful that it mentions homosexuality. The bylaws that spell out termination of an owners interest say nothing about personal opinions.
If you are buying a car and engage in a vicious racist rant should your car be repossessed? How about having your home overrun to force you out? How far should this be taken?
It will revolve specifically around agreements he made with the NBA and their bylaws. But I cannot imagine that any agreement would necessitate someone give up his rights to express himself privately. Nor could I imagine Sterling, who is a sharp guy, signing such a thing.