"It all worked out in the end"
This theme killing for the good of others is repeated throughout the novel, and the castaway story parallels the plan and actions of Adrian Veidt. Adrian fakes an alien invasion to end tensions between the US and Russia. He plans to blow up New York City and blame it on aliens, believing this will end the Cold War. Adrian had good intentions, but he took into his own hands something that was not meant to be handled by him.
"One more body amongst foundations makes little difference"
Rorschach is a complex character who will deliver justice at all costs. "Evil must be punished. People must be told," were some of his lasts words. Rorschach was killed by Adrian because he threatened to reveal his plan. "One more body amongst foundations makes little difference," he said as he urged Adrian to kill him. Just as the castaway killed the couple because he believed they would rat him out, Adrian killed Rorschach because Rorschach could not live without telling others of Adrian's plan.
"I did the right thing, didn't I?
Adrian killed three million people in order to save billions. Is this worth it? Does the end justify the means? This mirrors the trolley problem, where you can either kill five or pull the lever and kill one. Adrian chose to pull the lever and sacrifice one person instead of killing five. He meddled in business that was not his own, and quite possibly ended the situation with means far more drastic than necessary, which ended lives that probably didn't need to be ended.
"I leave it entirely in your hands"
The castaway story and the Adrian story seem to be perfect parallels, the only difference being the ending. We do not know what happens in the end of the Adrian story. We do know, however, that in the end of the castaway story, his plan was all for naught. If we assume the Adrian story is a perfect parallel, then that means these people were killed for nothing. Though Rorschach was killed, his journal lives on. Will his journal be published, revealing the truth and possibly re-sparking tensions between Russia and the US?