He stumbled on the last step, but he got up at once. "He even took care to brush off the dirt that was stuck to his guts," my Aunt Wene told me. Then he went into his house through the back door that had been open since six and fell on his face in the kitchen. (5.78)
Finally! The ending of Chronicle of a Death Foretold is the moment that we've been waiting for from the very first line. Even though we know about the motivations and details surrounding Santiago's death, we never actually see it occur. We only hear about it secondhand. But in these few paragraphs, we can see exactly what caused this town to deal with to cope with its guilt for decades after the event.
Marquez also uses these last moments as a way to reinforce the absurdity of the whole situation. He reminds us that the back door had been open the entire time, and that Santiago could have lived if he had simply gone around the back. We are never allowed to forget that this entire event was totally avoidable, even when we finally get the death scene we've been promised since the beginning of the story. It serves to remind us that, sure his death was foretold, but that doesn't mean it had to happen.