[Justice]

There are a few points I would question, or seek more information about, before any conclusion could be made. here is the first one that jumped out at me from what I read and remember.

According to Mormon, there were no Nephites or Lamanites that were “men of God,” during his tenure as commander of the Nephite nation.

This is not actually true. 4th Nephi ended about the year 321, which is the time period Mormon made that statement. This is the same time Ammaron hid up the plates in the hill Shim. Mormon was about 10, and was made leader of the Nephite army 5 years later. So, in about the year 326 Mormon writes:

WoMormon 1:
8 And it came to pass in this year there began to be a war between the Nephites, who consisted of the Nephites and the Jacobites and the Josephites and the Zoramites; and this war was between the Nephites, and the Lamanites and the Lemuelites and the Ishmaelites.

This was the beginning of the time of the great and last war referred to by Joseph Smith, 5 years after Mormon commented there were none righteous. Mormon had a church and was teaching and preaching. Moroni told of how they called priests and teachers and people were baptized. So, there began again to be righteous among them, including Moroni.

Now, this war began about 326 and lasted until about 385 and covered a large portion of the land "north." There's no telling exactly where it began and where it ended. It appears to me that Zelph was killed during this last and great battle that spanned from 321 to 385, and was killed when they crossed that spot of land as they were fleeing from the Lamanites. It does not mean he was alive and took place in the final battle of Cumorah. They may very well have ended up in New York before that last day when 320,000 of the Nephites were slain in a single day.