Me - Krishna, everybody has a purpose or mission to complete in life & after they complete the mission they die  right?

Krishna - Yes dear everybody has to die after their life's mission is complete.

Me - Then what about Astachiranjeevi (8 immortals)

Krishna - The Astachiranjeevi are immortal
because of the virtues or sins committed by them. And all the immortal are alive to help tenth incarnation of Vishnu , kalki to restore dharma or...