In Jacob 4, Jacob seems to have a clear knowledge that the words on the plates will be preserved:
1 Now behold, it came to pass that I, Jacob, having ministered much unto my people in word, (and I cannot write but a little of my words, because of the difficulty of engraving our words upon plates) and we know that the things which we write upon plates must remain;
2 But whatsoever things we write upon anything save it be upon plates must perish and vanish away; but we can write a few words upon plates, which will give our children, and also our beloved brethren, a small degree of knowledge concerning us, or concerning their fathers
Other prophets also seemed to know very well that their words would be used to judge the world. Both Nephi and Moroni close their writings with an acknowledgement of this fact.
Here's Nephi (from 2 Nephi 33):
7 I have charity for my people, and great faith in Christ that I shall meet many souls spotless at his judgment-seat.
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11 And if they are not the words of Christ, judge ye—for Christ will show unto you, with power and great glory, that they are his words, at the last day; and you and I shall stand face to face before his bar; and ye shall know that I have been commanded of him to write these things, notwithstanding my weakness.
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13 And now, my beloved brethren, all those who are of the house of Israel, and all ye ends of the earth, I speak unto you as the voice of one crying from the dust: Farewell until that great day shall come.
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15 For what I seal on earth, shall be brought against you at the judgment bar; for thus hath the Lord commanded me, and I must obey. Amen.
Nephi is not subtle in making his point. (Read the whole chapter to get a full sense of his boldness.)
And here's Moroni (from Moroni 10):
24 And now I speak unto all the ends of the earth—that if the day cometh that the power and gifts of God shall be done away among you, it shall be because of unbelief.
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27 And I exhort you to remember these things; for the time speedily cometh that ye shall know that I lie not, for ye shall see me at the bar of God; and the Lord God will say unto you: Did I not declare my words unto you, which were written by this man, like as one crying from the dead, yea, even as one speaking out of the dust?
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34 And now I bid unto all, farewell. I soon go to rest in the paradise of God, until my spirit and body shall again reunite, and I am brought forth triumphant through the air, to meet you before the pleasing bar of the great Jehovah, the Eternal Judge of both quick and dead. Amen.
Equally unsubtle.
One other note, Royal Skousen is convinced that the final sentence should say "pleading bar" instead of "pleasing bar" and I agree with him.