Vash doesn't die. The manga's storyline keeps him alive through all the challenges and adventures. The creators chose to give him a different fate than death.
Definitely not. Vash is a figment of someone's creative mind. It has no roots in true events. The entire concept is built from scratch for the purpose of providing an enjoyable and imaginative experience for viewers and readers.
Overall, Trigun Stampede adheres closely to the manga. Some minor details might differ for the sake of the adaptation's flow and visual presentation, but the core remains the same.