If the Nephites were destroyed in 385 AD, how could the desdendents of Joseph, presumably numbered with the Nephites, have survived this great battle?
It should be remembered that the division of the people into these two camps, the Nephites and the Lamanites, is a vast oversimplification. Jacob records, Now the people which were not Lamanites were Nephites; nevertheless, they were called Nephites, Jacobites, Josephites, Zoramites, Lamanites, Lemuelites, and Ishmaelites. I, Jacob, shall not hereafter distinguish them by these names, but I shall call them Lamanites that seek to destroy the people of Nephi and those who are friendly to Nephi I shall call Nephites, or the people of Nephi, according to the reigns of the kings (Jacob 1:12-13). The Book of Mormon record states that there were Lamanites among the Nephites and Nephites among the Lamanites. These had chosen their allegience based on religious and political lines and not racial lines. Therefore, it should not be surprising that the promise was given to Joseph that some of his seed would be preserved even after the final destruction of the Nephites. This means that some Josephites who had defected to the Lamanite side would merge with Lamanite society (see Alma 45:13) and the blood of Joseph would be preserved. DC 3:16-17 explains that the blood of Joseph, Jacob, Nephi and Zoram was preserved and that the testimony of the Book of Mormon was to come to their descendants in the last days.