I expect that even among those who say they will definitely withdraw all deposits, not all actually will. Reassuring statements by banks and banking authorities are plentiful and will be believed by some depositors. Coverage by the FDIC is being emphasized. Examples include a brochure and statement stuffer made available by the FDIC as well as other material on its web page . Non-physical withdrawals by some depositors.
Bank runs can take the form of adverse clearing balances as depositors shift funds to other banks.
This was the case with the Continental Illinois failure. The Federal Reserve can easily handle this type of run. It has established a Century Date Change Special Liquidity Facility as an additional means of helping banks cope with withdrawals. In the extreme case, regulatory authorities will limit cash withdrawals from financial institutions. I have begun tracking the rate of increase in currency in circulation .