Do you drop a story if one specific character dies?

[beast_regards]

Only if it is a decoy protagonist. It's rarely done in the way you would truly believe that one who died was the protagonist. The shows like Game of Thrones or Expanse have multiple story lines, so one of the major characters dying doesn't feel like it was the protagonist.

 

[BearlyAlive]

Kill them for all I care, but don't do it badly. The death of Ned in Game of Thrones was well done and set the pace and expectations, or at least in the books.
Killing the old mentor character because "mentors need to die" is just boring.

Killing a decoy MC to turn the whole story upside down and use the unreliable narration to invert everything the reader thought to know? That's an art form.