If all Banks in the world are emptied..? What would happen if every person in the world pulled their money out of their bank accounts?
The thing with these economics questions that never happened empirically is always the same: nobody really knows.
Befor Creditanstalt 1931 nobody thought that a bank can go bancrupt, during BrettonWoods/Goldstandard freely floating exchange rates were sought of being detrimental and dumb....

But in theory everything should collapse due to our fractional reserve system that requires banks to have a certain amount of money stored in their books for every granted loan.
But thats not going to happen because centralbanks would intervene and convince people that they are going to do anything to keep the banking system working. If the CB is able to make a trustworthy commitment that should work. Because a rational individual should have no incentive to have so much cash... The costs of carrying so much money are simply too high...

Once there was this Eric Canton attempt....