I was disappointed in the version of Cyrodill that was presented to us visually...lack of dragons, gondolas, and Battlemage aristocracy...
No Nibenese face tattoos either.
Face tattoos are the alpha and omega of TES lore.
With regards to the original question, I don't think it's ever been fully established. I've been with this series since just about the beginning, and I still have no idea if the "provinces" represent large administrative districts within the Empire or simply historical and ethnic regions. For example, High Rock seems to now be ruled by Daggerfall, Sentinel and Wayrest. Is there a "Governor of High Rock" above them, or is High Rock just the term for the region, like "the Balkans"?
It also doesn't help that the Empire is portrayed differently in the different games. In Daggerfall it was essentially powerless; Tamriel was ruled by a nominal Emperor, much like medieval France or the later Holy Roman Empire, but he had practically no real power outside of the Imperial Province. That's why he had to work through an agent. In Morrowind, the Empire was strong enough to be building forts in distant, contentious lands and much more closely resembled the classical Roman Empire in terms of structure. In Oblivion...?
Unfortunately, if any game was going to answer these questions, it would have been Oblivion. My own theory is that the Imperial presence in Morrowind was a still functioning relic of an earlier, stronger Empire and operated more or less independently by the time of the game. By the end of the 3rd era, the Empire lacked the power to do much in most of the other provinces. The Elder Council, made up of the richest and most powerful people in the individual provinces, functioned as the only meaningful liason between Imperial and local power, and even that was pretty illusionary. Thus the Emperor's death didn't really have much of an impact, except maybe to further isolate the provinces.
...so to answer your question, I don't know.