What if "dying" as an adult takes them back to the wilderness?
When Van is in the hospital, teen Van tells her about the plot of The Goonies. When adult Van asks if she's dying, teen Van tells her they're going "to find the treasure," but her mouth doesn't move when that is said.
I'm not a huge believer in the supernatural theory, BUT if it is supernatural, what if the "treasure" is being indefinitely confined to the spirit of the wilderness. Maybe that's what happened with Cabin Guy and that's why he appeared in the vision. Maybe all of the other characters who died there are still there "in spirit" and when they all die as adults, their spirits return. This is why "death" is always the plane crashing again, because they are returning.
Perhaps the show will end with all of the teen spirits back in the wilderness, finally all agreeing that the wilderness is the treasure, understanding that they can't escape its influence and therefore embracing it.