Fractional-reserve banking works not because commercial banks “pretend” still to have the money they already loaned. It works because the representation of that money by different bank accounts remains mistaken for the same deposit money, which hence replicates itself among its different representations by those different bank accounts (or notes, checks, etc), in what I call a representational monetary identity. Bitcoin prevents this by inherently distinguishing money (a private key) from its representation (a public key).
So you think you can have fractional-reserve banking without ever having central banking? Or that you can have central-banking without sooner or later having the deregulation of banking and the merge between commercial and investment banks? Or that you can have that merge without the explosion of derivatives?
Today, most money is debt. While the primary mechanism for debt becoming money (of which central banking is the first “derivative”) is this: when a commercial bank makes a loan, it creates new money that, if deposited into another bank account in the same or any other bank, enables the latter bank to loan it again, creating even more money. This continuous creation of debt expands the money supply that we use to buy cars, houses, and cell phones, creating inflation—so this credit money is as much an illusion as the cars, houses, and cell phones it buys, or inflation it causes. As some of us know, if everyone were to withdrawal their money from all banks, there would be no money left for most of us to withdrawal. However, this is no longer because of any fractional, say 10% reserves requirement, but rather because now less than half of that percentage exists in physical form—a percentage that continues to shrink.