In the 80s and 90s, Greek inflation was in the 15-20% range. Italy dropped to 5% more quickly but at the start of the 80s was in the 20% range.
In the 70s UK inflation was 10-20%.
that type of inflation is clearly bad for keeping cash, but not going to cause the collapse of civilisation. From about 73 - 80 US inflation was in the region of 10% per year.
The post you replied to said unstable or high inflation, not unusable. An unstable dollar will not instantly bring about the apocalypse, there are plenty of real life examples of unstable, high inflation currencies. The currencies took years to fully fail.
Not to mention, a few years of hyper-inflation don't even imply that the currency will fail.