We should still remember the righteous in Ammonihah who were similarly killed. Alma's comment at the time was, behold the Lord receiveth them up unto himself, in glory (Alma 14:11). And so it was with the martyrs of Anti-Nephi-Lehi, we have no reason to doubt but what they were saved.
Through mortal eyes, the death of 1005 innocent, helpless, righteous souls is a tragedy and a travesty. To the Lord God, it is according to his work and his glory, to bring to pass the immortality and eternal life of man (Moses 1:39), For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts (Isa 55:9). This is a great example of how the Lord uses a tragedy to save souls. Often, the spiritual benefits of tragedy and trials are not as immediately evident as they are in this remarkable story.
Thus we see that death is a tragedy to the mortal man but not to the Lord. The spiritually minded understand the word of the Lord when he said, fear not them which kill the body, but are not able to kill the souls: but rather fear him which is able to destroy both soul and body in hell (Matt 10:28).
Gordon B. Hinckley
"Notwithstanding the evil and the tragedy, I see a silver thread shining through the dark and bloody tapestry of conflict. I see the finger of the Lord plucking some good from the evil designs of the adversary." (Conference Report, Apr. 1968, p. 21 as taken from Latter-day Commentary on the Book of Mormon compiled by K. Douglas Bassett, p. 289)