Sci-Fi from the 70s-80s about the majority of the population vanishing, remaining ones developing telekinesis and similar powers and living for 1000+ years, then they discover the missing ones on other planets,

[Edward]

Help me find this one for a friend.

Something like 99% of the Earth's population disappears, and the remaining people somehow end up living extremely long lives (1000+ years) and developing powers like telekinesis and other powers like this.

Eventually, it is discovered that the others somehow ended up on a few different planets and they, too, live super long lives.

The only other hint that I have is that somewhere in the book there was a philosophical question similar to "how much would have Leonardo Da Vinci accomplished if he lived 1000 years?".