The Mormon Church’s Official Position
The LDS Church believes that one of its greatest strengths is that it is the only church that does not depend entirely on the Bible for its teachings.
"Had all the Bibles in the world been destroyed, the doctrines and teachings of the Church would have been found to conform to Bible teachings, since they were a received by direct revelation from God." - A Marvelous Work And A Wonder - Ch1, Pg1
That is wishful thinking. Had all the Bibles been destroyed in the world, there would be nothing to expose the "truth" the LDS Church professes. Well, except lack of archeological evidence for the death of the Lamanites and Nephites, the fraudulent translation of the book of Abraham, not to mention the implausible story of Joseph Smith hightailing away from greedy townspeople with a 200 lb golden bible for 3 miles.
Have you ever tried to carry something for 3 miles? I used to have to use a jackhammer for work to dig holes and it weighed about 50 lbs. and that thing was a beast to cart around. How far could you make it with someone chasing you as well? Did you know Joseph Smith walked with a limp due to a childhood infection?
So what are we to think of this claim? that extra information is needed for the direction of your eternal journey?
Here are a few comments that Jesus and Paul had about this.
Matthew 7:15 - Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves.
Matthew 24:24 - For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.
Matthew 24:35 - Heaven and earth shall pass away, but my words shall not pass away
2 Corinthians 11:13-15 - For such are false apostles, deceitful workers, transforming themselves into the apostles of Christ. And no marvel; for Satan himself is transformed into an angel of light. Therefore it is no great thing if his ministers also be transformed as the ministers of righteousness; whose end shall be according to their works.
In the end, we are given a very sincere command, for our own well being:
1 John 4:1 - Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
John is saying "WAKE UP!!!" don't empty your mind, use your God-given intellect. The devil is smart, and he's pretty good at role-playing.