Death is no longer a certainty.
Generic engineering gives humans potential lifespans of centuries. Even when the DNA starts to breakdown from repeated replication nanotech machines are capable of correcting and refreshing them giving a fresh start to the DNA and another century or more of life. The maximum 'natural' lifespan of humans is unknown but theoretically infinite.
Even that is just the beginning.
Given enough data storage and powerful enough scanning equipment it is possible to store the complete DNA record, the position and composition of every molecule and the relationship between every charge and force in the human body including the very mind.
If given that information and nanotech molecular contruction a person can be completely rebuilt. Without needing a piece of the old body. Complete physical destruction can be overcome. The same creature is built, same atoms in the same places, same neural structures holding the same memories. The same life.
It may be different atoms but then the materials in your body are completely recycled approximately every 7 years in normal natural growth.
The construction itself is simple. The human body is mostly made of relatively simple materials such as carbon and while complex is not more so than many common machines built in nano-factories and matter compilers. The data storage for a human however is immense, and expensive.
Usually only those who have proven themselves useful have the data storage capacity given to them that would allow them to be rebuilt.