Those hours are still available to you, should you need to use them.

The benefit that you still have is correctly called "Top Up":

Top-Up Benefits:
In addition to receiving value for your sick leave through the reimbursement of the DPMA/DPMA Equivalent premiums, your sick leave may also provide additional benefits to you. Whereas the reimbursement percentage was a one-time calculation, the receipt of “Top-Up” benefits will depend on how you use sick leave through your Delta career.
The NWA sick bank you carry over at DCC is charged 80 hours for each month you receive disability and DPMA/DPMA Equivalent payments, since the combination of these payments is equivalent to 80 hours of NWA sick leave. Top-up benefits will be paid to pilots who have a NWA sick bank balance remaining at the end of the DPMA/DPMA Equivalent payment period after being reduced at the rate of 80 hours per month for each month of DPMA payments. Top-up benefits are paid exactly like sick leave and will be paid until the NWA sick bank is exhausted or the pilot returns to flying status. In this way, a NWA pilot receives value for his sick leave hours.
Since DPMA/DPMA Equivalent coverage will supplement disability payment for up to 12 months, a pilot who has more than 960 hours (12 months of DPMA X 80 hours= 960) at the start of a disability period, will receive top-up benefits until the remaining NWA sick bank is exhausted. For example, a pilot with 1280 hours in his NWA sick bank at the start of a disability period will receive top-up benefits for an additional 4 months; 960 hours were deducted during the 12 months of DPMA coverage, leaving 320 hours for Top-Up benefits to be paid at 80 hours per month.
Summary
The focus of the JCBA negotiations was to identify a way for NWA pilots to transition into the Delta programs. We were very aware of the need to retain the value of our sick leave program, and believe that the two transition mechanisms discussed above—the reimbursement of DPMA/DPMA Equivalent premiums to represent pre-paid sick leave and the top-up to represent additional accumulated sick hours—provides significant, equivalent value to the NWA pilot population.
If you have any questions about this you should contact your ALPA rep or call the Delta MEC R&I Chairman.