Flight from Zion

Flight from Zion is a main quest $$ Instead of staying to fight for their home, the Courier chooses to help the Sorrows flee Zion. Alternatively, the player can take the opposite quest, Crush the White Legs, and destroy the White Legs and kill Salt-Upon-Wounds.

This quest, Prisoners of War, Retake the Bridge, and Sanctity of the Dead are received simultaneously.

Detailed walkthrough
The quest starts just south of the Caterpillar's Mound. Move towards the Sorrows Fork Campground and, from there, head towards the East Fork Bridge. There will be White Legs hidden atop cliffs along the paths, usually in threes. Once close enough to Pine Creek Tunnel, the first stage is completed. Salt-Upon-Wounds must then be dealt with. Up the road ahead, several Sorrows tribals will engage in battle with Salt-Upon-Wounds and two or three other White Legs.

Salt-Upon-Wounds approaches the Courier and initiates dialogue, stating his intent to kill them. There are two ways to end this. The Courier can say, "Let's end this, then," and initiate combat. Alternatively, with a Speech skill of 75, the Courier can tell him that there's "no reason this has to end in bloodshed." From here, more options become available, all of which result in Salt-Upon-Wounds leaving peacefully:

Once Salt-Upon-Wounds has been dealt with, Daniel must be spoken to. He asks if everyone has been accounted for. Saying "Yes, go!" will progress to the next stage of the quest. If the three side quests Prisoners of War, Sanctity of the Dead and Retake the Bridge have not been completed, they become permanently unavailable. Joshua Graham departs the Courier's company at this point in the quest.

The Courier is then given a Detonator that is set to detonate the C-4 placed above the mouth of the Pine Creek Tunnel. Firing the Detonator collapses the passage and prevents any White Legs from following Daniel and the Sorrows out of Zion. Once the C-4 has been detonated, the player receives the achievement/trophy May my Hand Forget its Skill, and then the ending sequence plays.

Bugs

 * Sometimes the optional quests will not show up in one's Pip-Boy.
 * Some Sorrows tribals may be left behind at the tunnel after the completion of this quest.