If everyone were instantly replaceable perhaps it wouldn't be strictly legal, but they are not. In Sydney, the numbers and licences have all gone into the same bucket so it seems.
I don't think it's that easy for them. There are 4 distinct departments in SYD, one of which is growing.
You can't make someone redundant, if the position remains! They should have shuffled all the decks before they announced the redundancies, if they wanted to get away with this!