What might have happened if scientist had not used the International System of Units during the construction of the international space station?

Answer 1

Nothing serious would have happened. They could have used Imperial measurements if they wanted to. Obviously it would be stupid if some suppliers used Metric to make parts , and other suppliers used Imperial. Scientists are not so silly as to allow anything to be made, without having a written specification for the precise details of every single measurement. They are certainly wise enough to demand the use of metric standards; not some other crazy standard such as Imperial. Metric (SI) system is used by almost every nation in the world except USA. But USA Scientists ALL use SI units. That has been happening for more than 100 years to the best of my knowledge.

Which system of measurements was used doesn't really matter as they all can be equally precise if the engineers working on the project are equally precise. What matters is that everyone uses the same system, or are proficient at converting from one system to the other. While a universally adopted set of standards may make building things easier, it certainly doesn't guarantee a higher degree of excellence in the finished product.