[vinceguidry]

I propose a different explanation for the continued circulation of shillings after the central bank collapsed. Social need. Since there was no available currency of worth for Somalians to use as a medium of exchange, they simply kept using shillings. Had there already been an alternative currency, say euros or dollars, shillings would have reduced in value and most trades of value would be going through the legitimate currency.

Rather than government backing or historical precedent, simple supply and demand propped up the shilling. Currency, even fiat currency, is not intrinsically worthless, it's useful on its own merits as providing a convenient alternative to bartering. This also explains why the counterfeits were accepted, people simply saw the warlords as providing liquidity that the government couldn't.

Once a government steps in with an alternative, the existing tender will slowly stop circulating. Or perhaps a mobile network may get froggy and offer cheap connectivity along with a payments network. Currency is like any other asset class.