Nearly a month has has passed and I had this question saved for a while, and only just bumped into it when purging my saved posts tab. Sorry I forgot to answer! Seeing as I can rehash old posts pretty easily to try to answer your question, I hope you don't mind my late response:

Let's begin at the beginning. The year is 476. The Western Roman Empire has lost Gaul (to the Franks) Iberia (to the Visigoths) and Africa (to the Vandals). Only Italy and Dalmatia continues to be ruled by Rome. Years of civil wars an infighting has decimated the army, and a long succession of army-backed strongmen have taken turns ruling the empire, many of whom have mixed Romano-German heritage; Romulus Augustulus, the last emperor, was a puppet of his father Orestes, the Magister Militum (head of the army). Although Orestes had married into a Roman family, he himself was not an ethnic Roman (to be pedantic, the Eastern Emperor never even recognized Augustulus, which allowed Julius Nepos, the pervious emperor, to rule in semi-autonomy in Dalmatia claiming all the while to be Emperor of the West).

Flavius Odoacer, the de facto leader of the Foederati or ethnic "Barbarians" fighting for Rome (who by now made up most of the army) deposed Romulus Augustulus when the emperor lost the majority of the army's favor (this was no cakewalk. Odoacer had to fight several pitched battles against armies commanded by Orestes and Orestes' brother). After coming to power, Odoacer openly admitted that although he might rule Italy, he was powerless beyond the alps, and consequentially didn't call himself Emperor. Instead, he sent the imperial paraphernalia to Constantinople and asked to be recognized as "Consul". Odoacer kept all of the functions of the Roman Administration in Italy intact, although there was a big political upheaval, there wasn't much of a cultural upheaval (Flavius Odoacer himself was so romanized historians aren't sure which "Barbarian" ethnic group he belonged to).

Odoacer initially played lip service to the previous emperor Julius Nepos, minting coinage in his name, but may have been involved in the plot whereby he was murdered. Regardless, after the murder of Julius Nepos, Odoacer asked to be given the title of Patrician by the Eastern Emperor, and be recognized as the ruler of Italy under the wing of a single Roman Emperor in Costantinople.

The Eastern Emperor Zeno, however, had his own issues to deal with involving "Barbarian" contingents in his army, namely involving two Ostrogoths both confusingly named Theodoric (this in addition to social, religious, and political unrest in his own half of the empire).

Although the Ostrogoths had been given lands in Pannonia in exchange for the defense of the upper Danube, Zeno came to the conclusion that the Ostrogoths were more trouble than they were worth (fighting with him, fighting with each other, and in a general sense just being another nuisance to deal with) so he convinced their King Theodoric to go conquer Italy. This way, they would stop annoying him, and he could also get rid of Odoacer, another potential opponent. Zeno could afford to lose Theodoric's army as the bulk of soldiers in the eastern empire were still "Romans", as the large recruiting grounds of Anatolia and Armenia were not yet subject do destabilization (using the word "Romans" as they themselves would have: to denote citizens of the empire).

Theodoric the Amal, King of the Ostrogoths, had been raised in Constantinople. His people were largely Romanized, having lived within the Eastern Empire's borders for centuries. When Theodoric defeated Odoacer and set up the first Kingdom of Italy, he did his utmost to further maintain the Roman institutions, law, and judicial system. However, he did not rule from Rome, rather, he ruled from Ravenna, seaside city conveniently defended by swampy surroundings, and easily supplied by ship.

So here we are, soon after the "Fall" of Rome, the first Kingdom of Italy was established as a client state of Costantinople, and lasted into the sixth century. One political system was substituted for another, and this new system was arguably better suited to the militarized necessities of the time. Although the apparatus of the state had long been in decline, there would be no "Shock" that would warrant a diaspora, as infighting among the Italian (or Italianized) ruling class continued much as it did for the past few centuries when the ruler of Italy was calling himself "Imperator" instead of "Rex".