This page of the guide lists all ways in which Jacob can die. Remember that the game features the "death rewind" option, which you can use if you die by accident.
Considering the content of this page, a spoiler warning is in order. Below, you will read about important choices and situations that happen during The Quarry's storyline. For obvious reasons, we had no way of avoiding spoilers, but we tried to describe the storyline as vaguely as possible, and only point to specific situations.
In chapter 4, Jacob may die at the hands of Ryan. Just shoot the bushes when you see a character in them. This way Jacob will be killed, and his body will not be found. To save Jacob, you simply must not shoot at the moving target.
In chapter 6, Jacob is chased by a werewolf in the woods. He will fall into a bear trap. He will die if you choose the "free yourself" option and perform the QTE sequences incorrectly.
In chapter 9, Jacob may be killed by the transformed Nick when he emerges from his cage in the basement of the Hackett house.
To save Jacob, you must first release Nick from the cage when playing as either Laura or Ryan in the basement. Simply select the option to try to rescue your friend, then open doors 1 and 2. Opening the cages will cause Laura to destroy the building's power source. You can's skip or avoid this moment.