We even learn that the mighty Mormon has been killed and except for Moroni this included all of the 24 who had survived the Cumorah massacre. The fact that Moroni says he is now alone and that it is 401 A.D.would suggest that his father may have been killed rather recently and being alone is a great trial to Moroni. The fact that he and his father were together in the not too distant past is suggested by verse 11, where Moroni says the three translated disciples of Jesus ministered to both of them.
One of the saddest lamentations in the entire Book of Mormon is Moroni's expression of grief when he says: "My father hath been slain in battle, and all my kinsfolk, and I have not friends nor whither to go." Where is his wife and children and all their friends? Where are the 10,000 valiant Nephites that were under Moroni's immediate command? They are all dead. Even his beloved father, Mormon, was killed.
You can tell that Moroni felt he was the loneliest man in the world. He is also very frustrated. He feels there is a lot of writing to be done but he has run out of space on the plates and has no ore to make more plates. His father had promised to translate the book of Ether, containing the history of the Jaredites, but he was killed before he could do it. Since Moroni has the Urim and Thummim he could do that translation but of course that would require ore to make the plates. Little does he know what will happen in the not too distant future.