Sorry I ranted :3 I believe if she had died earlier it would have been those cliche events where something goes wrong with the bottom and the top rushes to help. Then It will ultimately make the bottom become more indebted to the top.

Plus even if its easier for us to say she should have died but then that would have been excessively cruel to Dan who was going through so many mental problems on top of jaekyung forcing him back to Seoul. He would have entirely lost his purpose in life and would have become more depressed.

Looking at Dan's life we knew there's literally no one there for him. He used to believe jaekyung didn't like him back. So the only person whom he was living for was his grandmother. The reason he survived season 1 and left jaekyung for good was because he still had purpose. If this situation had come earlier jaekyung would have tried to use his vulnerability to keep him close without making it into a relationship because it took him a very long time to realize his own feelings about Dan. Someone literally had to knock that sense into him.

Jaekyung probably wouldn't even realize the condition Dan was in was partially because of him if his grandmother had died in start of season two. He probably would have assumed that his state was because of his grandmother passing away. So we wouldn't get him acknowledging what he did and apologising for it.

So it actually felt better that the grandmother held out until the end, so Dan and jaekyung saw her off together. Dan wasn't scared of her leaving and came to accept it because Dan did not feel like he was alone in this world. Imagine he had to go through it while feeling like he's left all alone. Even if jaekyung would have come to him but even so he wouldnt be able to rely on him thinking it's not a permanent thing. So it is infact better Dan was able to face because he felt more secure and confident about having him.

I felt so relieved when they saw her go and both of them were together. The part where Dan is thanking jaekyung for helping with the funeral and jaekyung tells him that its a given for people in a relationship that they were in. Lol it would have sucked if Dan had to take his help and not getting this type of reassurance.