Interesting - and not doubting what you're saying - in previous companies overseas there was a provision in the OM to continue but reduce pax numbers to the number of exits that could be used in an evacuation with reduced crew.
Seen this abroad too but CASA won't allow it here. Simply cannot operate unless crew numbers are adhered to CASA minimums which is 4 for your typical 180Y A320/737. Not uncommon to see longer domestics with an extra crew member also to potentially reduce the above risk which is quite costly to send it back empty/accomodate pax and possibly send another empty back to collect pax.
I thought they had a Darwin base?