When the time comes, everything's value, including fiat money, will be measured by bitcoin. People will talk about how much Satoshi a house worth, how much Satoshi a dinner cost etc... And Satoshi will be the universal scientific standard of value, just like meter and kilogram, it is mathematically complete
What is the standard unit of value, this purely depends on the majority of people's consensus. When that consensus is reached among billions of people, then the standard is established. But other standard could also co-exist, just like foot and pound were also used widely