In 50 years, I see Astro the same way I see Superman. Might not be as popular as he once was but would still a huge following, we'll continue to see new adaptations and he will always be an iconic character.
Another thing that seperates Astroboy from other manga titles is that while most mangas/animes have a ending (and the authors try to make sure when the story ends, it ends), you can still get new stories from Astroboy even though Tezuka isn't around anymore.