I can shed some light on how it is in the Qantas group with regard to cabin crew hours limitations.
An A380 very recently took off from Heathrow and returned for some technical issue after dumping fuel.
A number of the cabin crew decided that they could not work beyond 20 hours and elected to get off.
There were no replacement cabin crew available for the flight and the aircraft left some 12 hours or so later with a fresh crew.
Lots of very inconvenienced passengers including one, Alan Joyce.
Now, I have it on very good authority that severe criticisms were made of the crew by senior management [including the small Irishman] because an element of them felt that in this case they couldn't go beyond 20 hours.
I genuinely don't think that management consider that cabin crew fatigue or flight duty limitations have any bearing on safety.
When in the past I've had the temerity to questions ops over these types of issues [as they are occurring] I'm invariably fed their standard, "industrial agreement" line that goes like this-
" It's legal".