NCO burnout in Vietnam was focused heavily in the senior NCO ranks ("in the rear with the Sergeant Major, the beer, and the gear"). Remember that during this period most (if not all) of the Army's SNCOs had combat time in Korea and even World War II. It wasn't a problem initially, but by mid-1968 the Army was relying more and more on "shake and bake" NCOs (guys who were a handful of months or maybe a year older than the men they were supposed to train and lead). Older NCOs were either getting out or using their connections to get rear jobs.

Again, this trend accelerated as the war went on. It wasn't so much a factor of KIAs as it was repeat tours and (likely underestimated) a major "generation gap" between the Regular Army NCOs and a mostly draftee force fresh from the impact of the counter culture.

Within the canon, most of Kieth Nolan's books touch on the NCO issue in at least some way, since his writing focuses for the most part on the period after 1968. It's touched on to a degree in some of the SOG memoirs, but like I mentioned before the memoirs tend to come from either the junior enlisted or officer ranks. Shelby Stanton talks about it in "The Rise and Fall of an American Army" as well. "Self Destruction" also gets into it.