To paraphrase John Lennon, you may say Webb's a dreamer—except, as it turns out, he actually was the only one. The leader of the original five, he's the glue that holds them altogether, and his death is what makes them unravel and fall apart. Hannah writes in her book that "who they were had always been determined by him" (5.7), and Tate later foretells her and Fitz's own destiny by saying, "What happens to all of us when you're not okay? What then? We'll become pathetic" (8.8). Everyone needs Webb.
Webb's presence is intoxicating, and we don't just need to read Hannah's book to figure that out. Taylor can see it simply from looking at the photo of him Tate and Narnie took to the police station when he went missing: "It's not about his face, but the life force I can see in him. It's the smile and the pure promise of everything he has to offer" (18.46). He oozes vitality, it seems.
Although he's as emotionally scarred by the accident as the rest of them, Webb is the group's natural leader and the one who manages to continue planning their future in spite of his own grief. He makes plans to build the house by the river, begins the territory wars as a way to liven up a boring fall, and ultimately is so filled with hope after he dreams of his and Tate's daughter that he goes to sit in the tree and talk to her. Despite terrible loss, he makes it possible for the group to survive.
Here's the tragic thing about Webb, though: He's the only member of the original group that we don't get to see as an adult. Thinking about his character ultimately just brings us back to the tragedy of these kids' lives, particularly Fitz, who never meant to kill Webb, and Tate, who plunges into despair and leaves Jellicoe after Webb's death is confirmed.
In the present day, learning her father's identity gives Taylor a new sense of her own mortality: "Hannah once told me that there is something unnatural about being older than your father ever got to be," she says. "When you can say that at the age of seventeen, it's a different kind of devastating" (18.49). On the upside, perhaps somewhere in here Taylor derives a bit of the strength she cultivates to quit living in fear and start truly engaging with life.