The prospect of Sterling suing could be a source of worry to NBA owners for at least three reasons:
1. Sterling suing over franchise ouster could undermine the lifetime ban. The ban is intended to separate Sterling from the Clippers and the NBA, and as discussed above, Sterling likely has no viable case against it. If, however, Sterling sues over franchise ouster, it would be a high-profile lawsuit and he would remain in the news. Whatever distancing of Sterling is achieved through a ban could be lost in a high-profile case. It is also a case that could last years, as antitrust cases often do.
2. Sterling suing may lead to pretrial discovery, which could be designed in part to embarrass other owners and NBA officials of any bigoted remarks or beliefs on their part. Keep in mind, if Sterling is ousted because of racism, he would likely demand that evidence showing that other owners and officials are also racist be shared. He would use such information to portray his penalty as unwarranted and contradicted by the conduct of those who ousted him. Sterling might request emails and other records from owners and officials that depict them in a negative light. Sterling has owned the Clippers for 33 years, which suggests that he has had many interactions -- including private conversations with league officials and owners. If there are other owners who are racist or bigoted, it stands to reason Sterling knows who they are.
3. If Sterling wins or extracts a settlement, not only could NBA owners be on the hook for an expensive fee, but Sterling would seem victorious. The appearance of him winning in court would greatly detract from the important social message accomplished by the lifetime ban.