Yes, okay, we're under the assumption that Jackie is dead because she fell asleep outside in the snow. I mean, her body was basically frozen, but a few theories have been circling around that point to the fact that she could actually be alive. The most believable theory is based on her high school journal; if we look closely at her journal entries, she lists a few movies from later years even though the plane crash occurred in 1996.
For instance, in her journal page labeled, "Movie Character I Would Be," she wrote down Rose Dawson when The Titanic wasn't released until 1997, "Bring It On," which didn't come out until 2000, and American Beauty, which premiered in 1999. If it took them 19 months to be rescued, it would make sense that Jackie could've been watching some of those movies, meaning that she somehow survived her sleep in the snow.
In addition, when Shauna is reading through the journal in Episode 6, she has a possible flashback of Jackie, who's telling her, "It's not your fault—what happened. Actually, you don't know. It's totally your fault. But we were kids. And it was awful." This is following a flashback that Shauna had of the two of them together in her room, so it's unclear if this new scene with her is actually a flashback or just Shauna imagining her being there. However, Jackie is wearing the same clothes from the other flashback, which makes it seem plausible that it was a flashback from just a year or two after they were rescued.