What must happen to a mortgage upon successful payment of the debt?

When a mortgage loan is successfully paid off, the correct outcome is that it becomes void. This means that the borrower has fulfilled their obligation to the lender, and as a result, the lien that the mortgage created against the property is removed. The lender must then provide a discharge or satisfaction of mortgage document to the borrower, evidencing that the debt has been fully repaid and that the lien on the property is no longer valid.

In contrast to the other options, transferring the mortgage to a new owner would typically involve a situation where the mortgage is assumed, which is not directly related to the payoff process. An increase in value of the mortgage does not occur upon payment; instead, the borrower is relieved from the obligation. Additionally, a mortgage becoming subject to additional liens implies that there are new claims against the property, which contradicts the resolution of the existing debt. Overall, the successful payment of a mortgage eliminates that liability, leading to its void status.