The Viet Namese are not insane nor stupid. Indeed, throughout the war they showed enormous political and strategic intelligence. It is truly the case that they lost every battle except the last one, and that they won the war. I fully understand why people want closure on the lives or deaths of the people they know or love, but the fact that you want something doesn't mean that it's possible for you to get it. Men are lost without a trace in every war, but it's become far more common since the beginning of the 20th century.
War is a horrible thing, and human ingenuity has found many ways of killing people.
Some of the ways are extraordinarily violent and leave nothing to find. In France and Belgium, farmers unearth bones in their fields even now. They're skeletons left over from World War I, men who died in no man's land and were eaten by rats. In World War II, this became more common and the men listed as MIAs died all over the world. There are thousands of MIAs in Korea, too.