Although not very known outside of Russian-speaking people, I would recommend Sergey Lukyanenko. He deals with mortality/immortality in several of his novels: "

Although not very known outside of Russian-speaking people, I would recommend Sergey Lukyanenko. He deals with mortality/immortality in several of his novels: "Line of Delirium" [1] and "The Stars are Cold Toys" [2] dilogies immediately come to mind. [1] https://en.wikipedia.org/wiki/Line_of_Delirium https://en.wikipedia.org/wiki/Line_of_Delirium [2] https://en.wikipedia.org/wiki/The_Stars_Are_Cold_Toys https://en.wikipedia.org/wiki/The_Stars_Are_Cold_Toys