We can't forget that the only viable alternative for some 772 routes in the DL fleet is the currently smaller A359 fleet. The A339 can cover a few more, but combined with the A359 that fleet is currently only the same size as the 777 fleet. In order to truly replace the 777 fleet and retain the long-haul markets that the 777 was used for now and potentially in the future, it means DL will have to acquire that aircraft in the coming years. Talk about using working capital in a suspect manner.
In the short term there will absolutely be network cuts, but there's plenty of fat to trim even if DL doesn't want to eliminate too many destinations. MSP-AMS, DTW-AMS, and ATL-AMS are all 3x-4x daily in the summer. SEA-AMS, DTW-CDG, ATL-CDG, JFK-CDG, JFK-AMS, JFK-ATH, JFK-TLV, BOS-CDG, and BOS-AMS were all scheduled to be 2x daily this summer, with many of them seeing additional frequencies on AF/KL. I'd say there are easily 10+ frequencies that could be cut from that group of flights, with no route drops and little overall affect on the network, if DL so chooses.
Making some cuts from the above routes and maybe rearranging aircraft types on a few other TATL routes could free up enough of the newest batch of 10 HGW A330-300s to cover for the majority of 77E flying (the only 77E route those 333s might not be able to cover is ATL-HND, which I'd expect to go to the 359). That leaves the 77L routes, which would need to be cut or replaced with 359s. I think ATL-PVG will be cut. DL probably doesn't need to send their own metal on ATL-ICN either, and could move that frame to cover LAX-PVG or something. The 359s that were slated to serve MSP-AMS, DTW-AMS (x2), and ATL-AMS could be repurposed to cover 77L flying. I think there are many possibilities, and I expect DL network planners have the requisite creativity to think of them too.
As things start to recover over the coming years, DL will still be slated to receive 24 A350s, which should allow for plenty of re-expansion into gaps where routes need to be dropped temporarily.
This is my signature until I think of a better one.