Has an International Rugby game ever ended 43-9?
Exactly once. On August 23, 2003, England beat Wales 43-9, and no International Rugby game before or since has ended that way. When it happened it was a scorigami, the first 43-9 in league history.
That makes 43-9 the 510th most common final score out of 844 that have ever occurred in International Rugby. One point away, 44-9 has happened never and 43-10 has happened never.