We know that Moses was very מכיר טובה (grateful) even to inanimate objects: he didn't want to hit the dirt or Nile, etc.
Yitroh took care of Moses for decades and married his daughter to him.
After Matan Torah Yitro wen back to convert his people (the Midianites?)
When Moses waged the war against the Midianites, they explicitly killed every man and all women (see Numbers.31.7.
I don't recall Moses remembering Yitroh and his family.
So did he mention to spare the lives of the family of Yitro?