If that happened, do you think the people of Philadelphia themselves EVER referred to their city (or their Church) using the middle name of the Emperor of Rome? I doubt it.
I'm sure that while the Roman Governor may have referred to Philadelphia as Flavia, the people in Philadelphia probably referred to the Emperor as Flatulence but I doubt he would have answered to that name.
I also doubt very seriously if Jesus would have used the Roman emperor's name in a letter praising the Church that had been named the "Church at Philadelphia" even before Flavius Vesparian came to power.
And now you have Laodicea being destroyed at least 5 years before the earliest date anyone has given to the Book of Revelation. I dare say that most cities in that area were largely destroyed by earthquakes every decade or so and rebuilt upon the same ground. That was the nature of building and architecture back then. A 5.0 earthquake which would do little damage today would do major damage to unreinforced concrete or unreinforced brick or stone buildings. I'd say that within 30 years of 61 AD Laodicea would have been largely rebuilt (and probably knocked down again a couple of times in the interim).
Philadelphia sat in an important location. Expositor's Bible Commentary says, "About twenty-five miles southeast of Sardis, along the Hermus River valley, lay the important high plateau city of Philadelphia, modern Alasehir. A main highway that ran through the city connected Smyrna (about a hundred miles due west) to northwest Asia, Phrygia, and the east. Furthermore, the imperial post road of the first century A.D., which came from Rome via Troas, Adramyttium, Pergamum, and Sardis, passed through this valley and Philadelphia on the way to the east. So situated, Philadelphia became a strong fortress city. To the northeast was a great vine-growing district, which, along with textile and leather industries, contributed greatly to the city's prosperity."
The name Philadelphia came from the founder of the city, "Attalus II (159-138 B.C.), who had been given the epithet ‘Philadelphus' (brother lover)" because of his love for his brother (Expositor's Bible Commentary). But this was not the city's only name.
"Still another name of the city was Decapolis, because it was considered as one of the ten cities of the plain. A third name which it bore during the 1st cent. AD was Neo-kaisaria; it appears upon the coins struck during that period. During the reign of Vespasian, it was called Flavia. Its modern name, Ala-shehir, is considered by some to be a corruption of the Turkish words Allah-shehir, ‘the city of God,' but more likely it is a name given it from the reddish color of the soil.
"In addition to all of these names it sometimes bore the title of ‘Little Athens' because of the magnificence of the temples and other public buildings which adorned it. Philadelphia quickly became an important and wealthy trade center, for as the coast cities declined, it grew in power, and retained its importance even until late Byzantine times" (International Standard Bible Encylopaedia, Electronic Database, 1996, article "Philadelphia").
"According to Strabo, the whole region was earthquake prone (Geography 12.579; 13.628). In A.D. 17 an earthquake that destroyed Sardis and ten other cities also destroyed Philadelphia. Consequently, many people preferred to live in the rural area surrounding the city. The fear of earthquakes caused those who continued to live in the city to leave it at the slightest sign of a tremor.
"After the devastating earthquake, Tiberius came to the peoples' aid and had the city rebuilt. In gratitude the citizens renamed it Neocaesarea (‘New Caesar'). Later the name was changed to Flavia (A.D. 70-79), and this, along with Philadelphia, continued to be its name through the second and third centuries A.D…" (Expositor's Bible Commentary).