Has a FIBA World Cup game ever ended 90-49?
Exactly once. On November 27, 2017, Germany beat Austria 90-49, and no FIBA World Cup game before or since has ended that way. When it happened it was a scorigami, the first 90-49 in league history.
That makes 90-49 the 475th most common final score out of 1,178 that have ever occurred in FIBA World Cup. One point away, 91-49 has happened never and 90-50 has happened 3 times.