where do you think Qantas would have stood with every aviation hull insurer in the world if they'd knowingly put an aircraft back in the air that should have been written off.
Should have been written off economically, yes, but not due to the extent of the damage. QF wanted to avoid a hull loss so would have spent a heap of their own money to avoid that. Pretty much the same with a car that the insurers want to write off because it's uneconomic to repair but you can take their pay out, add some off your own moolah, and get it repaired.
Do you think they'd have put it back in the air if it wasn't insurable after the repairs? That it went back into the air means QF's standing with the aviation hull insurers was pretty good.