What do you think was the average K/D of a soldier who survived through a war

It varies so much and depends on how you break it down. For example, from quick googling there were an estimated 60-70 million allied soldiers in WW2. There were also an estimated 12 million axis casualties. So the average was way under 1.

If you looked just at US special forces numbers in Iraq and Afghanistan in the early 2000s it would be much higher than 1.