I don't see a world where Bitcoin is needed and it dies. So it needs to not be needed.
The only way to make Bitcoin not needed is for the world's problems to be solved. I don't mind living in that world either.
Discussion
But if we want to talk a realistic black swan event, even if it can't realistically turn into an actual threat to the protocol, is the centralisation of ASIC manufacturing. That being misused can make things bleak for a while.