In the final chapter of Chronicle of a Death Foretold, elaborate on the instances of how Santiago's death could have been prevented and on how it could have been prevented specifically from when his girlfriend's dad gave him the option to stay and hide or run.

In the final chapter of the book, Nahir Miguel warns Santiago Nasar that the Vicario brothers are planning to kill him. The text tells us that Santiago is more perplexed than frightened by the warning.
Nahir Miguel gives Santiago two options: either to hide in the Miguel home or to face the Vicario brothers with a rifle. Despite the warning, Santiago makes no concrete plans to protect himself. Here, we can see that Santiago would have lived had he taken up Nahir Miguel's offer of protection.
Instead, Santiago decides to leave the Miguel home. As he walks past the town square, he receives still more warnings from the townsfolk. Someone shouts at him to go by the old dock instead of heading home. Santiago chooses to ignore the advice. Then, Yamil Shaium yells at Santiago to seek refuge in his store while he looks for his hunting gun (and cartridges). At this time, there are many voices clamoring for Santiago's attention, but he decides to ignore them all.
Because Santiago cannot accept that there is an actual threat to his life, he becomes an open target to his murderers. If he had accepted the offers of protection from Yamil Shaium or Nahir Miguel, he might have succeeded in saving his life.
Going back to before Nahir Miguel's warning, we see that others also warned Santiago about the intentions of the Vicario brothers. For example, Clotilde Armenta gave her own warnings to Santiago. However, her words fell on deaf ears. Clotilde Armenta's husband (Don Rogelio de la Flor) probably voiced the real reason Santiago and many others refused to take the threat to Santiago's life seriously:

"Don't be silly," he said to her. "Those two aren't about to kill anybody, much less someone rich."

Meanwhile, the Vicario brothers did not keep their thirst for vengeance secret. They mentioned their intentions to more than a dozen people.
Just prior to the attack on Santiago, Clotilde Armenta grabbed Pedro Vicario and warned Santiago to run. Although Santiago did run when he finally saw the brothers approaching, he made the mistake of running for the front door. Just a few minutes prior, Placida Linero (Santiago's mother) had locked the door, believing that her son was inside the house. If the front door had not been locked, Santiago might have lived.
So, the above are many of the instances that describe how Santiago's death could have been prevented.