"Whatever plan you come up with (presumably better than the nonsense in the final film) would be unraveled by killing him later in the same film."

That's exactly what would make it unexpected, harrowing, exciting and poignant. That's what sets great storytelling apart from ordinary movies. As Nabokov famously made one of his great themes in criticism as well as composition, no artist should allow himself to get invested in and protective of his own characters. Once that happens, the story is being sacrificed for the characters, which upends the basic priorities of storytelling.