When that one mine runs out of salt? It will be closed. We as a humanity will not run out of salt, some places have the opposite problem: https://en.wikipedia.org/wiki/Monte_Kali

"According to the Werra Potash Mining Museum in Heringen, Monte Kali has been in operation since 1976; as of August 2016, it covered 98 hectares (240 acres) and contained approximately 201 million tonnes of salt, with another 900 tonnes being added every hour and 7.2 million tonnes a year."