I know I'm going to take a hit for this, one because I am a lawyer, and two because people hate lawyers and sports, but I think Cuban should sue Jordan, the Clippers, Doc Rivers personally, and Ballmer personally, as well as the NBA for allowing the transaction.
Contracts can't be signed until the 9th. I'd understand Jordan's point if that was a cooling down period so people didn't do anything stupid, but it isn't, it is a League issue for salary cap purposes.
There is a common law principle of verbal contracts which are contracts. They are not less of contracts than signed contracts, just harder to prove. Just like common law marriages are no less valid than any other marriage with a license, just harder to prove. They still have the same rights and obligations.
I don't think proving there was a verbal contract here is an issue. The issue becomes one of detrimental reliance. Were the Mavs hurt by detrimentally relying on Jordan's verbal contract. I'd have to say yes, and I think most others would say yes.
The hard part, and this is where lawyers come in, is proving damages. Normally, damages are the price it takes to fix the issue created by your detrimental reliance. Here, it isn't defined. Sure there are incidental expenses to finding a replacement player but those will largely be offset by the fact that a replacement player will cost less, since there aren't any available players at his position and ability. It really becomes an extremely interesting legal issue of what damages mean in monetary numbers of the value of a specific athletes worth and the missed opportunity of trying for another player who since committed elsewhere.
So, that covers Jordan. But what about the others? Once you establish there was a verbal contract, and it was widely reported and the Clips even accepted there was a verbal contract and stopped their pursuit of DeAndre until Jordan said he was having mixed feelings, there is a tort called tortuous interference of contract. That contract doesn't have to be written, it can be verbal. The reason it usually isn't verbal is because it is practicably impossible to know as a third party two people have a verbal contract and even harder to prove.
Here, it is pretty obvious that Rivers, Ballmer, the Clippers and the NBA knew there was a verbal contract between the Mavs and Jordan. I don't think that is hard to prove at all. The fact that they are actively interfering with that contract is an unbelievably awesome legal argument as it relates to sports.
Again though, proving they are tortfeasers isn't the hard part, but defining and assigning damages.
Like I said, I'm a lawyer and find these questions fascinating so I'd sue to find out the answers. Whether Cuban finds it as interesting and money worthy would be a totally different matter. While legally it is awesome, businesswise it might not be the best course of action.