I think you need to separate the two issues in your head - leaving your husband and leaving the country.
You simply will not be permitted to leave the country permanently with your children without DH's permission, not even if you engineer a fake holiday. The longer term scenario of waiting until he sees the light, gets a job in the UK and then you refuse to come back to Australia is just fantasy land - and it also would mean knowingly living a lie for possibly several years.
Frankly though it sounds like you don't like your husband, maybe even despise him, and certainly resent him. You can't make him go back to the UK. You can only do what is best for you and the DCs. From where I'm standing, that seems to be separating from your DH and making a go of life in Australia as a single mum.
That being said, children grow up fast and when they turn 18 you and they can make their/your own decisions about where you live. Living in Australia doesn't have to be a life sentence any more.
I'd also suggest you are, possibly quite unexpectedly given all your links with and experience of Australia, suffering from culture shock. When I emigrated from Oz to the UK it took me two whole years to feel like I'd made any friends and four to feel at home. Now I love it in the UK and would never go back.
What I'm saying is that you need to separate the issues in your mind. Do you want to stay with DH, regardless of where in the world that is? If not, you don't have to. You will have to stay in Australia for a bit for your DCs, but it won't be forever and you may soon find you love it. Think of all the upsides.