We need a lawyer's opinion.
I am not one, but would suggest that in order to get a conviction, it would have to be proved that they went back to DXB intending not to return to be interviewed.
I also presume that the crew has the right to be accompanied by a representative of their employer and their union (if any). In the meantime, where would they be expected to remain? In the hangar, in MEL, in Victoria, in Australia....?
I guess the important thing is whether they are prepared to cooperate if requested. That has not been disproved.
Compare with this: "The Australian Transport Safety Bureau has confirmed that QANTAS removed a flight recorder from the 747 involved in the accident in Bangkok in September 1999. A Senate Committee heard that the quick access recorder, one of the three black boxes, was removed from QF1 and brought back to Australia"