I think there may be something to be said for this. Part of the purpose of art is figuring out what we're doing here, what we even are, where our value lies. That means thinking about not only where we "go" after we die, but if our lives have purpose or value beyond that point and if so, how do we do the most with the life we have. All this is to say, part of the human experience is wrestling with the concept of Death.
Great books can help us do that.
This also extends beyond just physical death, I think. Think of Holden Caulfield. To a certain extent we are worried for his physical life, worried he might even kill himself at some points. But beyond that, even if his body continues to live, one could say that he's on the verge of suicide of the soul. A sort of emotional death.
In that sense, one could say that all the books we write, all the struggles our characters are facing, should be life or death. Maybe its actual, physical death, maybe its the death of a dream or a belief or an idol. Thinking of it that way may help get the tension we're looking for.
What do you think? Does this apply to your favorite book?