How Long Should A Story Last? Endings as Capstones

At what point should we decide that a story has gone on "too long"? One of the most important aspects of a story is its ending, which can make or break a story. However, in addition to many writers failing to write a complex and satisfying conclusion, a few exploit their series far past their prime and do not write the ending to a story they should have concluded long ago.

Stigma of the Wind just kept going until its author died, leaving behind no conclusion.

To begin with authors that end their novels poorly, Haruki Murakami is one of the most notable, due to the stark contrast between his ability to write rising action and climaxes compared to the flimsy excuses of endings that he provides to them. After Dark is notable for telling a compelling tale of people experiencing supernatural, yet unmistakably human, occurrences in the dead of night. His metaphors are surreal yet natural and the provide for a suspenseful story throughout. Then, it abruptly ends. An innumerable number of loose ends are left lying on the ground, with only a single potential character relationship being established while everyone moves on with their lives. 

His novel 1Q84 was powerful and suspenseful, displaying the subtle insecurities of the lead characters supported by deep and interesting side characters. Then the ending happened and everything went to hell. Characters began randomly disappearing, one was encased in an "air chrysalis", plot points that suspended the climax amounted to nothing, and almost no issues regarding the world of 1Q84 were resolved. 

Murakami himself in an interview stated that he "doesn't write endings".

Haruki Murakami, one of the greatest worst writers of endings.

That's a pretty glaring flaw. In most of Murakami's stories, the plot falls apart because there is no ending capable of melding their elements together. He leaves it open ended and engaging but not memorable. I can't go back to one of Murakami's stories, say "this was wonderful", and then re-read the book and relive the action. In this sense, Twilight finds itself superior (as a memorable story). Though far inferior in terms of its execution, one of the most important aspects about the novel and the series itself was that it produced characters that, while they were comparatively shallow, stuck in the minds of the readers. And I attribute this to a narrative having a strong ending; when it came down to it, I cared more about Edward than I ever cared about Tengo in 1Q84, simply because Tengo just disappeared into the distance without resolving a single problem while Edward tried his best and ended his first book in satisfying fashion.

Endings should be fairly abstract, no doubt about that. But endings that are too abstract are meaningless, with too many valid interpretations for them to even mean moot. In turn, endings that are too concrete are too boring because they do not draw the reader in to ask any questions at all.