At my work, I had to give 4 weeks notice as to whether or not I will be returning. So basically if I do return, I have to ring and tell them 4 weeks before and say I want to return, or I give 4 weeks notice of my resignation if I dont want to come back.
They told me this is "standard" so it might be the same rule for you too?
I had to give them 10 weeks notice of my intention to take leave, and then give them 4 weeks notice of the exact date I was starting my leave.
You can look on the industrial relations website for NSW and that will give you the info on what you should be entitled to.