I would echo the comment about getting legal advice. In terms of a 457, you are entitled to be paid your return fares when you make that request - it doesn't have to be redundancy. With respect to possessions, I suspect that will be at your cost unless you have a specific clause that says otherwise.
In terms of the redundancy and possible withdrawal due to a contract win, they would be able to do that in the UK and if you then said you didn't want it (assuming it is the same role), you would effectively be resigning, but get advice on the situation in Oz.
Whilst it is a horrible situation to be in, if they did do that, wouldn't you want to stay with them, at least for the time being, or have you made your mind up to leave Oz.
BTW, Sorry this has happened to you.