Quick discussion this afternoon (Sunday) suggests that if the lockout was premeditated, and Qantas accepted money for tickets after the decision to shut down the airline was made, then they have not been acting in good faith.
The outcome of that, if it is true, will be a class action lawsuit by stranded passengers against Qantas on Monday morning. You cannot take money for a service you have no intention of providing. Joyce, and the Board, have shot themsleves in the foot.
For all legal attacks there is a set of defences, and they have already presented it. Their claim is that their action was by economic force majeure. It is a common law defence, and is judged by the actions of a reasonable person in their situation.
As such in judging it they must look at it from the view point of a corporate director in that current situation, where the brand is being public bashed. Their responsibilities is to the shareholders as a whole, not individually (the creditors only in special situations but not an issue at this time). As such they are have a legal responsibility to minimise the damage to the shareholder's investments. If they can show the actions from the unions caused economic damage to the brand, as that the continued action would be greater than what occurred then they have a defence. FWA have already accepted it as part of their ruling so most courts would throw out any such action unless a error can be shown.