I think over half my lifetime Delta miles are on routes that no longer exist.
I flew CVG-ZRH at least 20 times. I had at least 16 trips to Japan, mostly PDX-NRT, but also PDX-Nagoya and LAX-NRT.
One of my favorites: AMS-STR.
I've also flown JFK-ARN, JFK-MAN, JFK-MUC (many times), JFK-CPH, JFK-STR, and some other European ones I don't remember.
SJC-CVG (short-lived).
SJC-DFW (my first Delta flight, in 1990).
SFO-PDX.
SFO-LAX.
OAK-DFW
OAK-SLC (on a real plane)
now that I think about it, and if you add the defunct SR and AY codeshares, about 90% of my Delta flying was on routes that were dropped.