Yeah, cause that pile of Deutschmark dad buried in our back yard was such a great idea. Lasted all of 54 years as a currency with "inherent stability". At least they will still take them in exchange for Euro "indefinitely", or until they change their minds.
Inherent stability, long term or not, is NOT a requirement for a currency to be useful. Just ask Argentina, Zimbabwe, heck, even China has to manipulate the hell out of the world markets to keep their currency "stable". All of those, and really EVERY currency that isn't the current "Reserve Currency" is still valuable to people making exchanges with it every day for food, shelter, work, etc. Maybe not AS valuable as the reserve currency in the world market, or in the home country of that currency, but still useful as a measure of portable, convertible value.