It really all boils down to that release clause amount.
If they can get FIFA to sign off on it not existing then they will be OK.
That's what happened with our underage signings CAS arbitration - we asked the FA and FIFA to agree with our opinion on the laws. They agreed and then couldn't touch us when it later went to CAS.
@tolmie's hairdoo said Messi's people had opened legal proceedings with FIFA. If what they are trying is to get a legal opinion from FIFA agreeing with their interpretation of the release clause then its a no brained, we sign him and settle for <75m later.