He’s not leaving his family. He’s going with them to Australia. His wife and kids are his main family. Parents and siblings are just extended family and take backseat at best once you are married. If he doesn’t look at it that way, he’s the one in the wrong. Sounds like he had an expectation that she would give up her extended family and didn’t even consider that she might want to move back there. But she was also in the wrong for not making that fact clear early on. Then again, maybe she mentioned it and it never sank in with him. Who knows?
Before I married my wife who was over here from China on a student visa, we discussed this issue. I told her I was willing to live in China for a few years after we first got married but that I wanted to return to live permanently in the USA. I also told her we could try to visit China together every 2-3 years but that she could go back more often if she wanted. She told me that she had no desire to live in China again and that she’d be happy to just visit every few years. In the subsequent 16 years of marriage, we have gone over together just three times and she has gone by herself just two other times. Typical visit is just two weeks. Her parents have also visited us in the US twice. She is happy with things the way they are. So am I, though I would have liked to have tried to live over there for a short while. And once I retire if she changes her mind about living there, I’d probably still be willing to give it a go. She’s my family.