How is zakat nisab estimated if gold is no longer in circulation, or, in other words, how is zakat nisab calculated without reference to gold or silver?

The nisab (threshold) for monetary assets is the equivalent of 85 grams of pure gold or 595 grams of pure silver. If gold and silver were hypothetically non-existent (which is an inconceivable scenario), then the nisab would be equivalent to half the value of five camels or forty sheep, based on the Prophet Muhammad's (peace be upon him) consideration of two sheep being equivalent to twenty dirhams for zakat purposes. A Muslim should focus on practical matters and avoid far-fetched assumptions that rarely occur.