Answer: Did anyone witness Lot's wife turning into a pillar of salt? The short answer to this question is that many times we must have faith that a biblical event actually occurred. No human, after all, witnessed God creating the universe or him making Adam. Countless other events recorded in the Bible must ultimately be accepted as valid and true based on faith.
It should be noted Lot's wife did not miraculously become salt for merely taking a quick glance behind her to see the destruction of her home in Sodom. The English word "look" used to describe her action in Genesis 19:17 and 26, comes from the Hebrew nabat (Strong's Concordance #H5027), which means to look intently in a favorable manner.
Lot's wife was punished by being turned into a salt pillar because she viewed longingly and regrettably at the destruction of the two great cities. Her attitude about Sodom, and her willingness to minimize their gross sins that brought their punishment, may have rubbed off on her daughters.
The attitudes of their mother could have played a part in Lot's daughters willingness to soon do whatever it took to ensure they would have children (see Genesis 19:30 - 38). Her attitude certainly played a large role in her own destruction through salt.
The Family Hesitates
Lot himself, not surprisingly, hesitated as he left Sodom.
But he (Lot) lingered, so the men (the angels appearing as men) laid hold upon his hand, and upon the hand of his wife, and upon the hands of his two daughters . . . and they brought him forth and set him outside the city (Genesis 19:16, HBFV).
The angels, as the group dashes out of Sodom, tell the family the following.
"Escape for your life! Do not look behind you, nor stay anywhere in the plain. Escape to the mountain lest you be consumed." (Genesis 19:17).
When the family finally reaches the small town of Zoar, just as the sun is rising, a destructive supernatural event takes place!
Then the Lord rained upon Sodom and upon Gomorrah brimstone and fire, from the Lord out of heaven . . . But his (Lot's) wife looked back from behind him, and she became a pillar of salt. (Genesis 19:24, 26).
As a side note, many Bible commentaries say that as she longingly gazed at Sodom she may have turned into salt from all burning or molten sulphur (translated as "brimstone" in the King James Bible) that fell on her from the sky. They state that what fell on her may have crystallized her into a pillar.
A Possible Witness
Lot likely witnessed the miraculously demise of his wife. It is only natural for the person in the lead to glance back to insure the rest were following him. Unfortunately, this loss was not the end of his trials and troubles. Right after God's judgment of his mate, his two daughters carried out a misguided plan they thought would insure the continuation of the human race (Genesis 19:30 - 38).
The turning of someone into a pillar of salt was such a significant event that Jesus used it as an example of what not to do just before his Second Coming back to earth.
And it was the same way in the days of Lot: they were eating, they were drinking . . . But on the day that Lot went out from Sodom, it rained fire and sulphur from heaven and destroyed them all . . . Remember Lot's wife (Luke 17:28 - 29, 32, HBFV).