The humans are not immortal, they die after some time. The humans die by countless different means, but most humans die through old age.
The human body was programmed to live for a certain number of years – on average 70 – and then fail to function gradually, resulting in the eventual death of the human.
The humans may also die through injuries or diseases which occur much earlier in their lives.
Sadly, there are too many causes of human death and the humans rank very low on the survival quota meter.