Anyone booking Sydney for Christmas is being wildly optimistic that they will be allowed to fly without prohibitive restrictions on both arrival in Aus and return to the UK.
I just don't see long-haul returning in any meaningful sense any time soon and it, sadly, may never return to 2019 levels.
It's going to take 2 years (perhaps longer) to 'sort' Coronavirus on a global level and then probably another 2 years before passenger confidence fully returns. Testing is not a solution - people won't book if the entire holiday hangs on a negative PCR test result, against the not insignificant chance of a false positive. And who wants to pay 5k for a holiday only to spend it treating other humans as a biohazard.
Mrs Le Chiffre works for a global blue chip and used to make regular trips to the States. The same operational and business 'effect' is now being delivered by MS Teams - and the company is saving 3 lots of round trips business class + hotels and expenses a year. Multiply this by the hundreds of employees in the same boat and, all of a sudden, they have a whopping saving on overheads.
BA are going to have to down-size and re-invent themselves with a focus on short and medium haul. This will almost certainly result in a further round of job losses or part-time / seasonal contracts (Easyjet have already gone down this route).