What is the ruling on a man saying to his wife: "If you don't return, then you are divorced"?

This is a conditional divorce based on the wife's failure to return to the country. If the condition is specified by a certain time—whether explicitly stated, intended, or indicated by the circumstances—and the wife does not return within that time, then the divorce occurs. If it is not specified by a time, the divorce does not occur as long as return is possible. However, if return becomes certainly impossible or highly probable to be impossible, then the divorce occurs at that point. It is advisable to consult the Sharia court.