Your analogy breaks down.

The difference is that with the cars there is no expectation that they will ever again be worth $1M. But the T-bills *will* be worth that amount again... they will be worth their face value at redemption time.

You are right that there will be more circulating currency for a period until that redemption time. But if those depositors that had a run on the bank, take their deposits and put them into another solvent bank, who then buys T-bills with the money... hey, they just took that cash back out of circulation right away!