No-one can prove or disprove the existence of God.

By the expression, 'God is dead', the philosopher meant that in the West, people had stopped believing in that entire structure of ethics and morality, with repercussions in eternity for breaking rules. Thus the externally-validated order by which to live and interact with others, had been fatally undermined, and nothing had been put in its place to form a coherent organising principle for both the individual psyche and the larger society.