Some seem to believe that natural death will be conquered, leading to not immortality but a life that will end at some point in a violent death, either accidental or otherwise. Some have calculated that the average would be 300 years with the longest life around 600 before the law of averages dictates a death from UNnatural causes. They usually don’t seem to think they themselves will be part of it but one wouldn’t actually have to see it happen all at once. If there is enough of a breakthrough to add twenty years to the average lifespan then one could hope that within twenty years there would be another breakthrough and so on until the final triumph over disease and aging. Where there is life there is hope, I suppose. Of course attaining even semi-immortality would create a whole host of new problems.
Then there is the question of why we should want to live five hundred years. The way things are going lately it just doesn’t seem like such a wonderful goal.
I can’t imagine the institution of marriage would last when longevity reaches 100 years, let alone 500.