So it all comes down to the last three T20I games, starting with the first on Friday on the same pitch at North Sydney Oval, under lights. If England lose then the next two games will be academic, but if they win then the battle will continue at the Manuka Oval in Canberra, two days later, and, if needed, two further days after that.
England will choose their starting XI from the same 15 players that have been selected for the whole series. It is doubtful there will be many changes in personnel, but Alex Hartley may get the nod this time ahead of Sophie Ecclestone, and Georgia Elwiss may have muscled her way back into contention, after showing some character with the bat in the Test, if not speed.
We will have a better idea of what is in Mark Robinson's mind when England play the Governor General's XI at Drummoyne Oval on Wednesday evening.
The fact that Nicole Bolton has been given the job of captaining the young GG's XI side may be an indicator that she will not be included in the full Australian side to play on Friday. Indeed Australia are yet to name their T20 squad.
It would be no surprise to see Alyssa Healy back up into the opener's spot, perhaps accompanying Beth Mooney this time. As well as the usual candidates I'd expect to see a couple of young guns named in the squad and perhaps even making the final XI. Heather Graham, Georgia Redmayne, and Molly Strano could all be hearing from coach Mott in the next 24 hours or so. Existing youngsters Ash Gardner, Tahlia McGrath, Lauren Cheatle (if recovered from injury - she is named to play in the GG XI game?), and Amanda-Jade Wellington are also likely to feature on Friday, meaning some of the more established faces may have to give way, as Australia look to build their T20 squad for next year's World Cup in the West Indies. Under threat are Elyse Villani, Alex Blackwell, Jess Jonassen and even skipper Rachael Haynes. It is doubtful all would go en masse, as the side needs some experienced campaigners, but I'd expect to see some fresh faces in the squad, and out on the park if Australia win either the first or second game and have the Ashes safely back under lock and key.
England haven't played a T20 game since their series against Pakistan in the summer of 2016. The Aussies last series was against New Zealand in February of this year - a series that they lost 2-1. With everything riding on it it should be a nail-biting affair, with the pressure perhaps more on the Aussies to get over the line, as everyone expects them to do, than on England, who know their chances of winning all three games are pretty low. Of course if England should win the first, and then the second games then the pressure will shift to them in the third, as they get to within touching distance of an unlikely Ashes Series win. It could all be in the mind!