NBA should void the contract.
Whether or not Jordan "signed" it is not the issue. This is clear circumvention of the established CBA and salary cap.
The league is lucky that Cuban simply let most of this matter go. Cuban is a media force now to be reckoned with , and in bed business wise with a lot of entities that deal with the league and the networks that broadcast the games. Cuban could have simply leveraged all that to bear against the NBA.
My take is Ballmer spent 2 billion, so this is his "mulligan" ( the league could have hit the Clippers much worse, if this was the NFL, the league would have gone pure scorched Earth here) Cuban simply weighed out adding to the embarrassment of the league administration and the ripple into the coming labor war when the net change would be none.
Karma is coming for the Clippers here. Journalist Charles Pierce said it best, you might hate Donald Sterling, you might loathe his views, but part and parcel, fundamentally did the NBA just strip a team and sell it for 2 billion to increase valuation of all NBA teams under the pretext of being offended by a person they tolerated for 20 years knowing who and what he was, trampling the concept of free speech, even if repugnant, along with it.
I don't hate the Clippers as much as the Patriots, but it's pretty damn close.