If the Bulldogs were to sue SBW, his manager and Toulon then it would only partly be about his wages. It's more to do with the damage done to the club by his walking out. This means things like merchandise sales, sponsorship opportunities, even the fact that him not being their impacts upon their ability to make the play offs and win trophies. There is a lot of money at stake there, so he could end up paying through the nose for a long time to come.
That of course is through the civil courts. If it went to the Court for Arbitration in Sport then SBW wouldn't have a leg to stand on. He's signed a contract to play for the Bulldogs, anything signed beyond that would be invalid.