DL does plan to phase its MD11s out over time, but was not in the rush that AA and some other carriers were in to rid itself of the type.
DL still has some work-rule issues to finalize with its unions concerning its 777 operations.....that is why the MD11s still fly the Japan routes and flew the long TLV and Cairo routes until those routes were discontinued. You may remember that DL actually parked newly delieved 777s for a while, a few years ago, until a compromise was made with the pilots to get the planes into the air.
When will the 777 totally replace the MD11? Not sure, firstly, DL wants to make some money before placing another large order for the type. The other issue is with UPS, I had read that DL and UPS entered into an agreement for UPS to take the MD11s over time, later in the decade.......I am not sure of the status of that agreement at this point, a lot has happened since 9/11. Maybe a DL expert can help us with this issue.