Some of the excavated ruined houses showed signs of former vertical shafts that were dug down into them, presumably by the owners (or under their orders) to retrieve cash or personal papers or whatnot. It's at least somewhat possible that some of those roofs lasted long enough, and survivors hidden inside the homes dug their way out. OTOH, these shafts may have been to search for missing family members.
It was formerly believed that the beginning of the eruption scared off most of the people in the Bay of Naples, and no remains had ever been found in Herculaneum, which was right on the slopes. Then in the last couple of decades of the 20th century, a group of remains were found in a newly-discovered storage room on what had been the Roman-era harbor. Apparently they were waiting for evac, or just found that to be the only available shelter.
The cities were damaged years earlier by the earthquake, which was probably a precursor of the eruption itself. While the population of Pompeii at one time may have been 20,000, there may not have been that many living there in 79 AD. The House of the Vettii was about 200 years old when it was buried and ruined, and by that time was owned by a couple of freedmen. Down the street, in another house, the owner's lending records were found, and the owners of the House of the Vettii were among his clients/borrowers.
Unfinished repairs from the quake are still in evidence. I wouldn't be too surprised if it turns out that most of Pompeii was semi-abandoned by the time of the eruption, and social rankings had changed a great deal. The imperial period was one of upward mobility, opportunity, wealth, and of course ostentatious displays, kinda like the rap/hiphop industry today.
Entirely plausible. On youtube there is a narrated video of a walking tour of Pompeii. It is nearly 5 hours in length! Search for “prowalk tours Pompeii”. It is incredibly informative and I highly recommend it.
CC