We have just been through a similar situation.
If you’ve lived in Wentworth Falls prior to renting it remains your PPOR up to 6 years. I don’t know about coming back to live in it. (I think ruling is on the ATO site) You have to pay CGT on Mt Isa or CGT on Wentworth for the time you owned Mt Isa – it’s a tricky calculation and you need a good real estate accountant. We paid on our first PPOR that we had rented out when we left to work interstate and it looks like it was the best way to go.
