On the surface, the possibility that he might not be rescued adds to Decoud's sense of futility. But this is a multi-layered line relating also to his search for the self. Recall that in his argument with Antonia, his penultimate suggestion was that one could, like Nostromo, live for and idealize the self only. With his dwindling life Decoud is trying to establish the same sort of grounding here, and failing. Hence "Nostromo was dead," meaning also the possibility of that sort of saving self-idealization.

Antonia, too, had rejected that possibility, leading to Decoud's ultimate suggestion, that idealism could reside in love. But...