I'm not sure if there's still a SHA-LJG nonstop which would be the ideal thing if available and if using moondog's suggestions to pry open a seat would work. Or if they'll do a connection routing via KMG or CTU for only one award. Failing that, the other Plan B options I see:
--CZ6799 PVG-KMG then overland, though ticketing for train to Lijiang still will be dicey thru Feb except maybe last week. Solves one problem but creates new one.
--As above to KMG then scrap Lijiang/TLG and go to Yuanyang per my previous suggestion. Depends on your interest.
--Pick a different place that CZ flies to nonstop and which isn't buried in deep winter: SHA-KWL possible but I thought you'd been there already. PVG/SHA-KWE possible but that time of year isn't great for minority village exploration and doesn't sound like your trip focus this time.
--Get a cheap Spring Airlines flight SHA-CAN out of pocket then you'd have more choice of point-to-point on CZ. Comes with caveats of flying an LCC, including schedule delay risk....and wastes time.
--If MU will free up seats but not for LJG, try Zhangjiajie (DYG) if you haven't been there yet. Typically flights in/out of there are expensive for the distance so might be a decent value. 5 days is about exactly right to see and hike Wulingyuan park + Tianmenshan, and go down to Fenghuang & Dehang.
--There's always the strategy of getting to Chengdu and heading for things you haven't seen before (if any of those remain, not sure where you've been besides JZG and Siguniangshan).
--Forget about using DL miles entirely if it seems too much of a force-job and/or the mileage value of the award after YQ is lackluster. Maybe there's a better use somewhere else. Must you stay inside mainland China for these 5 days? There's no shortage of places to go in the PRC but in February so many of them make for lousy destinations.