At first i cried reading the ending thinking this ended like the first time he was in the hospital and yellow dragon never came, however upon re-reading i realized that wasn’t it at all. The beginning of chpt 70 made it clear that he knew he wasnt going to be able to go back as long as he was alive and thats why he told his niece that yellow dragon was waiting for him, not the other way around. He told yellow dragon that he would wait for him so that yellow dragon wouldn't become evil again and yellow dragon gave him a ring from a piece of the pearl so when he finally did die his soul went back with yellow dragon. It is literally one of the happiest endings i have read because dojin got to see his niece grown up, he lived a happy life as the yellow dragon wanted for him and they get to be together eternally.
Whew that boy down bad for some kangjin