If you die without a valid Will, you are deemed to have died intestate. In those circumstances, a list of beneficiaries of the estate will be determined by the statutory scheme of intestacy in each State. In your case it would be the South Australian statutory scheme.
For example if you leave behind a spouse/defacto and no children, then your spouse/defacto will receive the remainder of your estate. If you also have a child or children and a spouse/defacto then your residuary estate will be divided as follows:

If the total estate is less than $100,000 the spouse or defacto receive the entire estate.

If the total estate is more than $100,000 the spouse or defacto receive:

-The personal chattels of the deceased

-$100,000 from the estate and 50% of the remaining estate

-The right to purchase the estate property

Child/ren receives:

-An equal share of the remainder of the estate
The statutory scheme will further detail the beneficiaries of your estate in the event you die intestate.
However, it is always recommended that you have a valid Will in place to avoid potential problems after your death.