It is important to point out that the bonds purchased by the RBA will have to be repaid by the government at maturity. They will have to be repaid in exactly the same way as would occur if the bonds were held by others. The same is true for the ongoing coupon payments on the bonds.
The fact that the RBA is holding some bonds makes no difference to the financial obligations of the government, other than through a lower cost of finance. The Australian Government and the states and territories continue to fund themselves in the market, as they should. Raising funds in the market is an important discipline and movements in market prices can contain valuable information.