Not sure what KES is thinking but I'll try:
(1) Fish-eating: Rather typical of k-dramas, especially of sad ending -- perhaps to soften the impact after a hard blow they deliver into our guts? They did that in Moonlovers Scarlet Heart ... Hae Soo & Wang So are split apart by centuries (literally-speaking), so the last scene was a flash-back of King WS having fun piggy-backing Lady HS -- which left us scratching our heads going "What Gives??!! "
Look at it this way: I had to put my cat to sleep -- her death is devastating but I will always remember our great times together. EC caught fish for AS to eat ~ oh so romantic; my cat caught dead mouse for me ~ and freaked me out ... TWICE! Still I miss her and it had been fun.
(2) DM's Death: He is already in bad shape, probably never recovered from that injury, only used opium to suppress pain -- death is inevitable, just a question of how. I prefer to believe that the writer chose to take him out in a more glorious way -- DM has some good in him. That said, DM had been ruthless -- killing indiscriminately at times. It cannot go unpunished, so his body is dragged, which is humiliating. Why not fight for Chosun and die honorably? -- that is not the DM we know.
Death ... if you are a good guy, hopefully you die with dignity or honor (go down fighting) and bestowed a nice burial; if you are an A-hole, then you die lamely (Mori, LWI) or your body is treated disrespectfully.
* We are optimistic people, we continue to believe there is hope despite all the hints:
~ Sad Ending -- the phrase that keep appearing
~ HN admonishes AS that because she chose to pick up the gun, she has caused harm to 3 men
~ HS carries the burden of his ancestor's cruelty. Chinese believe that among the 3 great sins, the worst is to have no descendants (Chinese thinking has a lot of influence on the Koreans and Japanese) -- HS's death is punishment of their evil deeds
~ EC's repeatedly stated to God that he is willing to exchange his life for AS -- hence EC has willed his LOVE for AS to LIVE
* I remember a comment about Star Wars Rogue One: We knew they (the Rebels) would die, but we didn't think they would ALL die !! I guess it's the same with Mr Sunshine ~ AS (a parallel to Princess Leia perhaps) is someone of the future generation and has to be alive to lead.
What more can we ask for EC?
A son of Chosun by birth, a naturalized American by choice, an ex-soldier who died bravely and honorably, remembered by many fondly, buried in the foreigners' plot but in Chosun soil.
Sad ending it may be, but I grudgingly admit, it did close out appropriately.