SgtBundy,
There is no CASA enforcement that cannot be appealed legally. That applies to this matter as well. Barrier could have tested the legality of the CASA decision and because of the implications of being shut down, a court will move rapidly to conduct at least an interim hearing to determine whether or not the initial CASA action should stand until a full hearing can be undertaken.
A company that I once worked for was deemed to be conducting RPT operations and had their AOC suspended. The same day the company lodged a notice of appeal that invoked an automatic stay. A hearing was conducted about a month later to determine whether a stay of proceedings should be made. In the meantime the company was able to continue trading.
Caper P/L v CASA
Now I have some serious doubts about the AAT as the appropriate forum to test aviation matters but that is another argument. Suffice to say that there are avenues that an aggrieved operator has but it costs and it may be phyrric victory.