There are no historical accounts of people leaving Pompeii as a precaution, and no reason to believe an eruption was expected by anyone. Take for instance this letter from Pliny the Younger to Cornelius Tacitus [0], who provides the only written accounts of the eruption. Pliny witnessed the eruption from Misenum, on the other side of Vesuvius from Pompeii across the Bay of Naples. He mentions how tremors were not considered a cause for concern, and he only describes panicked fleeing as the eruption itself is taking place. By the way, the uncle he mentions is Pliny the Elder, who was in charge of the Roman Fleet in the area and who died attempting to rescue a friend of his from Stabiae, another town which was destroyed by the eruption but not quite as fulminantly as Pompeii.

My uncle having left us, I spent such time as was left on my studies (it was on their account indeed that I had stopped behind), till it was time for my bath. After which I went to supper, and then fell into a short and uneasy sleep. There had been noticed for many days before a trembling of the earth, which did not alarm us much, as this is quite an ordinary occurrence in Campania; but it was so particularly violent that night that it not only shook but actually overturned, as it would seem, everything about us. My mother rushed into my chamber, where she found me rising, in order to awaken her. We sat down in the open court of the house, which occupied a small space between the buildings and the sea. As I was at that time but eighteen years of age, I know not whether I should call my behaviour, in this dangerous juncture, courage or folly; but I took up Livy, and amused myself with turning over that author, and even making extracts from him, as if I had been perfectly at my leisure. Just then, a friend of my uncle's, who had lately come to him from Spain, joined us, and observing me sitting by my mother with a book in my hand, reproved her for her calmness, and me at the same time for my careless security: nevertheless I went on with my author. Though it was now morning, the light was still exceedingly faint and doubtful; the buildings all around us tottered, and though we stood upon open ground, yet as the place was narrow and confined, there was no remaining without imminent danger: we therefore resolved to quit the town. A panic-stricken crowd followed us, and (as to a mind distracted with terror every suggestion seems more prudent than its own) pressed on us in dense array to drive us forward as we came out. Being at a convenient distance from the houses, we stood still, in the midst of a most dangerous and dreadful scene. The chariots, which we had ordered to be drawn out, were so agitated backwards and forwards, though upon the most level ground, that we could not keep them steady, even by supporting them with large stones. The sea seemed to roll back upon itself, and to be driven from its banks by the convulsive motion of the earth; it is certain at least the shore was considerably enlarged, and several sea animals were left upon it. On the other side, a black and dreadful cloud, broken with rapid, zigzag flashes, revealed behind it variously shaped masses of flame: these last were like sheet-lightning, but much larger. Upon this our Spanish friend, whom I mentioned above, addressing himself to my mother and me with great energy and urgency: "If your brother," he said, "if your uncle be safe, he certainly wishes you may be so too; but if he perished, it was his desire, no doubt, that you might both survive him: why therefore do you delay your escape a moment?" We could never think of our own safety, we said, while we were uncertain of his.

[0] https://gutenberg.org/files/2811/2811-h/2811-h.htm#link2H_4_...