It's the journey and the characters' endeavors that are most imperative, not the goal/ending.
You read it , right ? but why you didn't understand the meaning of the story........
Buddy, that's practically shakeasperean, someone goes insane and kills everyone else, it's a tragedy, thats a real ending for a story because theres none to keep the story going.

Honestly, what was the purpose of this manga....If most of the people that the stories were about died