Worldview Discussion - Death

So many questions related to death:

What happens when we die?
How do we know?
Can we know?
How does what happens after death affect how we live?
If there is nothing after death, is there true justice?
Who gets to decide when someone dies?
Is euthanasia morally permissible?
For materialists/naturalists/atheists - if evolution is true and we are all just "matter in motion" and there is nothing after death, why do we grieve when someone close to us dies? What evolutionary purpose does grief have?