Here the original manuscript is not extant for the predicate “are considered as dead”. Both the 1830 edition and the printer’s manuscript read are, so the original manuscript undoubtedly read are. The 1837 edition reads or, which is probably a typo rather than due to editing (are and or are visually similar and were thus mixed up by the 1837 typesetter). The RLDS text continues to have or here (although 𝓟 reads are). The 1879 LDS edition restored the original are to the LDS text, probably by reference to the 1830 edition.
It is possible that the original text read or and that Oliver Cowdery misheard Joseph Smith’s or as are. If so, the original text here reads as an incomplete sentence since the or ends up creating a present participial fragment (“being cut off from the presence of the Lord or considered as dead”). The critical text will maintain the are of the two earliest extant sources, 𝓟 and the 1830 edition.
Summary: Accept are as the most probable reading of the original manuscript in Helaman 14:16; the 1837 change to or creates an awkward sentence fragment and was undoubtedly a typo.