During the movie, Harold tries to figure out what kind of story he's in, a comedy or a tragedy, based on his interactions with the rebellious baker, and concludes it's a tragedy because of all the bad things happening to him. You realize later that while it's arguable he was being a victim of Comedic Sociopathy, and is in fact in a comedy, another solution is he's in a Romance instead, if you go by the classical definition (think (The Tempest), with his meeting of his own author making for his own Genre Shift. All it took was this quote: "I brought you flours." Say this out loud, "I brought you flowers."
Somebody did die at the end, but it wasn't Harold. The story was as also about the wristwatch, which was introduced as a character in the beginning. It was "killed" by the bus.
As pointed out in Fridge Logic, Eiffel seems to write several scenes in which a knowledge of the fact that Harold can hear her would be necessary in order for the scene to turn out the way it did (notably his phone call to her). This makes a sort of multi-layered, uber-meta sense when one considers the idea that the movie we are watching is the rewrite of the book Doctor Hilbert discusses at the film's end, edited to include Eiffel's shocking discovery that Harold can hear her.
Furthermore, the fact that she does not know where her story is going is characteristic of many writing processes, especially those who do not know how they want their story to end.
The fact that Harold Crick's life has been one of strict routine could be directly related to Eiffel's long spell of writer's block. If her narration is making his life happen, then it could be that her writer's block is the cause of Harold having a dull regimented routine for so long. If, instead, she's unconsciously drawing inspiration from his life, she could have been stuck leading up to the start of this movie due to Harold's insistence on having such a regimented routine. In either event, her voice popping up in his head could have been the only way around that block.
The phrase "little did he know" crops up at several points. Even his death was basically stated as being contingent upon him not knowing about it: "Little did he know that this small, seemingly innocuous act would result in his death" Knowing that he was going to die is part of what leads him to step in front of the bus to save that child, which prompts Karen to spare him. The knowledge of his death, which he wasn't supposed to have according to the story, ended up saving his life.
It should be noted that this is not an uncommon worry for writers, of contemporary fiction or otherwise, to have lurking somewhere in the back of their mind. If you've ever wondered why so many authors seem to have a love affair with impossible or incongruous names, part of the reason is to dodge this particular bullet since the probability of an actual person having that name, and thus being affected, is ridiculously low.
You also have to wonder if her other characters (if they were as real as Harold) also heard her voice. Did they think they were going crazy?
Several of the narrated actions of Harold Crick are actually caused by Harold's reactions to the narration, such as his Rage Against the Heavens, and his decision to make a phone call which ended up being to Eiffel leaving the viewer to wonder what Eiffel thought was the reason for Harold doing these things since she's not aware that he can hear her. You would have to accept that she was compelled to write it after Harold's actions started changing the actual plot. As addressed in Fridge Brilliance, this lead to her re-writing it after the fact.