At any time you can simply pay the outstanding balance and the Contract of Sale is complete. There are no restrictions that keep you locked in for 30 years.
Depending on your own circumstances you may at some point in the future be able to qualify for a traditional bank loan and get the bank to provide the money to pay out your Contract of Sale.
In fact many of our clients use Low Deposit Property as a stepping stone to enter the traditional banking system. They diligently create a strong payment history and then they refinance their Contract of Sale with a traditional bank loan.