It is my understanding that we each come into this incarnation with a Life Purpose.
Some people connect to it and express it throughout their lives, some never uncover it.
When we have completed our Life Purpose, or our 'mission', we will find a way to dispose of our body, be it a sudden heart attack or accident, a long debilitating illness, or any other form of disconnection that leads us to the ultimate transition from this life to another realm.