The novel ends with Doctor Monygham arriving at the Great Isabel to relay news of Nostromo's death to the Violas. Hearing the news, Linda declares that she will never forget him. In fact, she screams it out into the night, using his real (!) first name: "Never! Gian' Battista!" (III.13.153).
With that, the novel wraps things up pretty quickly:
Dr. Monygham, pulling round in the police-galley, heard the name pass over his head. It was another of Nostromo's triumphs, the greatest, the most enviable, the most sinister of all. In that true cry of undying passion that seemed to ring aloud from Punta Mala to Azuera and away to the bright line of the horizon, overhung by a big white cloud shining like a mass of solid silver, the genius of the magnificent Capataz de Cargadores dominated the dark gulf containing his conquests of treasure and love. (III.13.153)
The ending is kind of brilliant in a few ways:
First of all, it brings everything full circle with the mention of Punta Mala and the Azuera peninsula, which are mentioned in the first chapter.
Secondly, unlike at the beginning of the novel, Nostromo is front and center—and getting his name (and his real name at that) screamed from the rooftops (er, lighthouse). Just like he always wanted.
Thirdly, it drops in the word "conquests." The idea of conquest has been super important in the book, in terms of understanding the political scuffles and resentments that have caused Costaguana's wars. It's interesting that Nostromo has become a conqueror, right?
Finally, this ending also drops in that other little key word: "Silver." That might be the most important thing in the book, so it's notable the clouds above the landscape are likened to "a mass of solid silver." Dang. Even the clouds have a touch of the silver-fever by the end.
It's truly kind of amazing how Conrad brings references to all those themes and symbols together in just a couple lines. But hey, that's why he's said to have influenced such shining stars of literature as Virginia Woolf, Albert Camus, William Faulkner, and T.S. Eliot. He's amazing.