It could not, because it would have been:
1 A Logistical nightmare, especially with the techonlogies of the time.
2 An Administrative beast.
3 It woudl have required an economical effort that woudl have far oughtweighted the benefits.
Quite a generic answer. I find it unsatisfying and lacking in logic. How comes the Roman Empire lasted as long as it did, then?
After all, Roman logistics and administration became better with time, not worse. (Roman roads, administrative reforms, etc.) It's not like the mediterranean became harder to sail, or the roads harder to walk, after 100s of years of Roman rule. If anything, those difficulties had been solved already by the Republican army and the administration of Octavian.
Personally, I think the reason you saw a collapse of the old mediterranean-centered world in the 5th-8th century was that you had (1.) a higher growth of barbarian populations beyond Rome's frontiers, than among the Roman-ruled populations; (2.) a steady improvement in barbarian social organization, triggered by the rising population densities in barbarian lands, and catalyzed by the interaction with the Roman frontier; and (3.) a crisis in governance in the Roman empire at a time when the barbarians were numerous and powerful, which led to the invasions of 407 A.D. and the following years, that turned the western Empire into a warzone and led to the collapse of that half of the Empire; and (5.) devastating plagues in the 6th century (plague of Justinian) which hit the urbanized eastern mediterranean disproportionally harder than the de-urbanized western regions, and undercut the ongoing Roman effort to reconquer the western lands.
If Justinian had succeeded in breaking the barbarians and reconquering the west (and if the plagues hadn't killed off a third of the population), that could have been a re-invention of the empire, that would have turned the tides of history. They might have suffered conquests from another side later on (Arabs, Franks, Avars) but if a Roman state organization had been re-established successfully in Spain and Italy, those regions could have mightily stabilized the empire when the next wave of conquests rolled on. France was arguably lost, but Spain and Italy were still nice regions, that could have been turned into provinces once again, like Africa was.
When I compare the mediterranean world to China, which was a region united into one empire quite early and then re-united time and time again, the biggest difference I see is geography.
The mediterranean has the inland sea which connects everything, while China is a huge land region - you can get around in the mediterranean faster than in ancient China. But the mediterranean lacks the immense contiguous agricultural regions that China has in its riverine regions, where you have provinces that are as densely populated as the richest parts of the mediterranean world, but stretch for hundreds of miles more in each direction. Those regions in China were always full of people and largely flat, meaning you could easily conquer immensely huge populations and then there was little stopping you from overrunning your smaller neighbours. Much easier conquest than in the mediterranean world, where population centers are smaller regions, divided by the sea, and large armies cannot really live off the land when they traverse from one region into another (like they can in China). So the battles fought in the ancient mediterranean world are fought by rather small armies, compared with ancient China. Tiny, almost. The wars of the 3rd century BC, that ended when Qin had conquered everything, were mind-bogglingly huge with armies counting in the 100,000s, formed by drafting immense numbers of peasants and training most of them only rudimentarily, hurled against each other and ending with sickening massacres. There are regions in China where they still dig up 2000 year old mass graves every couple of years.
And then you have the thing, that "China proper" almost always encompassed all the densely populated lands, and its frontiers ran along jungles, mountains, deserts and the sea. (Of course those frontiers moved with time, and many jungle regions were turned into densely populated farmlands.) If any of the non-Chinese peoples was to conquer China, it would invariably always be the horse-born Steppe peoples, who would seek to rule China but invariably end up assimilating into Chinese culture, thus not un-making China but merely adding new pages to an ongoing history of an eternal realm.
Whereas "Rome proper" was an empire which had no such natural boundaries: In the north, it sort of petered out on the British isles, with Hadrian's wall dividing thinly populated, barely civilized northern England rather arbitrarily from barely populated, uncivilized Scotland. On the continent, the Rhine was the frontier, but rather for logistic reasons than because it made sense as a cultural divide. Arable regions continued far and wide east of the Rhine, which in the 1st century AD they had been hardly cultivated at all for lack of people, but over time became homelands of numerous and well armed barbarian peoples. Same thing on the Balkans - there was just sooooo much land north of the Danube, arbirarily divided from the Roman Balkans, and the barbarian lands filled up with barbarian peoples over time.
And then there was Persia, which was the eternal enemy in the east, equally powerful and civilized as the Roman empire. That frontier tied up a lot of forces. And from Persia, the Seljuks rode forth who eventually unmade the Roman Empire in the east. It wasn't a desert region populated by uncultured Steppe conquerors - rather, Persia was a civilized urban empire whose people were quite fond of their own civilizational model, who carried that model (modified by Islam) with them into Anatolia, when they conquered it.
So, the Roman empire has geography all set up against its longevity. It could have gone on forever if Germany and the northern Balkan had been less hospitable to agrarian lifestyles. If those lands had spawned only nomad peoples like the Huns, Avars, Pechenegs or (original) Bulgars, then those could have washed over the empire and perhaps ruled it for a while, but they could never have un-made Roman civilization the way the Germanic and Slavic conquests did. We'd still speak Latin to this day, and argue over whether the Avarii dynasty or the Hunnii dynasty were better at promoting Roman culture in Africa.
