The book doesn't say whether Sylvie and Richie die. I don't think it really matters. The main thing is that they lived. They took the time that they had and made the most of it. Many of us seem to just go day to day, without really thinking about how amazing it is that we're our hearts are beating. I think if we all lived like reckless teenagers on their deathbeds, the world would be a much more colorful place.