Ending 1 - Sacrifice | Game endings Dying Light: The Following Guide

If you decided to choose this ending, you must select the left option (Q button for PC - the above screenshot) during the conversation with the Mother, during The Following story-related quest. This will mean that you want to sacrifice yourself in order to prevent the virus from spreading any further.

The room with the nuclear warhead that you must arm.

Follow the Mother to the room with the nuclear warhead inside. You must arm the explosive by interacting with it. Crane will use the access code acquired earlier in the game. The game will end as soon as the nuclear warhead explodes.