The only thing that's certain about This Is Us is that nothing ever happens the way we expect it to — but that doesn't stop us from trying to figure out what's going to happen next anyway. With the midseason finale looming, it feels like Jack's story in Vietnam is about to reveal how Nicky dies, but in true This Is Us fashion, the show might be setting us up for another twist.
Nicky is in a terrible place right now. He's detoxing from drug use, and because of the traumas that he's experienced, he doesn't trust anyone in the village, including the women and children. In Nicky's eyes, everyone is the enemy, including the Vietnamese woman who gave Jack his beloved necklace. Back in season two, Jack tells Kevin that he received the necklace during a hopeless period in his life, which suggests that Jack is right about the woman — she is a good person caught in a bad situation. But to Nicky, she's just another person with the potential to hurt American soldiers, including his brother, which could mean he's about to do something stupid and senseless that will lead to his death — at least in Jack's eyes.
It's no secret that fans believe Nicky is still alive. The most common suspicion is that Jack either truly believes his brother died in Vietnam, or he's going to help him go AWOL. However, there is a third option. What if Nicky does something so terrible that it makes Jack believe that his little brother, who couldn't even hurt a bee when he was a kid, is dead in spirit, if not in body. And that terrible thing could very well be killing the Vietnamese woman, or letting her die, since Nicky is a medic. In the Thanksgiving episode, he refuses to help her son, which angers Jack, and also reveals to him just how far gone his little brother is. Jack doesn't like to give up on people, but the scene where Nicky explains how an old woman helped kill a fellow soldier makes it clear that the younger Pearson is never going to be that innocent little boy anymore.
Given how pivotal the necklace is in Jack and Kevin's stories, it wouldn't make sense for the woman to be setting Jack up. If she tries to hurt him, why would he hold onto the necklace or pass it down to his son? Her gift seems to have given Jack hope during a period of time when he had none. But it could also be a reminder of why it's better to believe the best in people rather than the worst, even in the darkest of circumstances.
Nicky no longer possesses the gift to see the good in people first, and that may lead to him killing this woman who gave his brother something positive to hold onto during his time in Vietnam. It's unlikely that the younger Pearson would murder her without some form of premeditation — even This Is Us won't go that dark. But all he needs to do is believe that she's a threat to Jack in order to justify ending her life, or if she's somehow injured during a skirmish in the village, he may simply watch her die. It would be a heartbreaking twist that puts Jack in a terrible position.
No matter what, Jack loves his brother, but if Nicky does something so brutal, he may realise he can't save Nicky from himself. If that's the case, Jack may end up letting his little brother go, and telling everyone that Nicky died in Vietnam, because ultimately, that would be much kinder than telling his parents that their youngest son murdered someone. It would also play into what Jack's Army friend told Kevin before he embarked on his trip to Vietnam: he may find out things about his father that Jack never wanted him to know. Don't be surprised if one of those things is that he lied to everyone about Nicky, and helped him avoid punishment for causing someone's death.
This also puts Kevin in a unique position in the present. He's in Vietnam looking for the woman, but he may find his uncle, and one dark story from his father's past, instead.