I recall a German lady talking about her husband who had been killed in 1945 -- she said when she thought about how much different life is now than it was 70 years ago, the new technology and all the changes and everything that has happened since WW2, and how strange it is to always think about her deceased husband in the context of distant past, to never hear his thoughts on the changing world and so forth, to think of him forever trapped in 1945.
I can only imagine how much more difficult it would be to cope and find closure when your loved one has been MIA.
Many times MIA was used when nothing of the body could be found, such as after artillery or bomb strikes.
One of my Dad’s friends was MIA on Tarawa. Later it came out that a Japanese artillery shell took out him and two other Marines.