If that were the case how do you think the company could get the last scheduled flight out fully crewed. Crew would simply call sick for that first sector and produce even more chaos.

Evidently there will be empty outbound cabins from London in the first days of the strike in order to repatriate the crew and commercial passengers on return flights. How long they might continue that with the extended days/leg patterns SIN/BKK to Sydney I dont know. Perhaps they will ferry them on other carriers, though there will be precious few seats available those days. Perhaps the cargo business will justify flying certain routes and of course there will be some staff who will still report for duty enabling some sort of skeleton service.