Depositors receive fixed return, bank uses depositors' funds to buy assets. Just set the real money supply equal to this real money demand to find a determinate price level. N.B. Fama's spaceship analogy.
People decide they like currency more.
The government requires banks to hold a minimum percentage of T-bills. A helicopter drops currency evenly over the economy. Proximately, the customers' decision to re-arrange their portfolio. No, although real macroeconomic problems could induce a run. Simple storage without deterioration.