There were 600 guys who disappeared in Laos and Cambodia; not a single one of them was repatriated. One former POW (Col. Ted Guy?) stated that from the time he was taken into captivity until he finally arrived in Hanoi, it was obvious he was "expected" at every stop along the way, and that there is no way every single one of those 600 could have disappeared without a trace.
Here is a list of 324 who were shot down, for whom there are reasonable indications that they reached the ground alive and in reasonably good condition.
What happened to them?