1) Yes it is on ticket issued by QF.
2) That's what they currently have, ie arrive in the evening back from Athens and then leave for Tokyo the next afternoon.
3) No, what they are actually considering is avoiding Athens completely and getting a charter flight back from one of the neighbouring islands direct to London. This save nearly a days train/bus/ferry travel to get to Athens. Thus they are not too worried about moving the date forward, which they may be able to do, space permitting. The biggest worry is cancelling of onward flights.