Obviously Palpatine himself only wanted power and the Sith to rise to prominence, but wouldn't the fascist government he built under him have some kind of nationalist equivalent ideology? It's possible that would keep them together after Palpatine died, but I admit I am not a historian and don't know the parallels. I guess the ones I do know, a central figure was essential, so meh.
Well, at least in the last two centuries there have basically been two kinds of autocratic nationalists: the ones who won and succeeded in their wars and population purges and the ones who didn't. The former generally rule as "lifetime" leaders (read: until the next coup), but they also tend to so completely traumatize their population that whatever form of rule comes next at least makes
some changes to the system of governance; the latter generally end up dead or exiled, which gives the general populace a convenient scapegoat ("I never wanted to be a soldier in the Nazi Army, I was just afraid of the consequences of not going along with Hitler, please don't execute me for war-crimes"). Populations do occasionally coalesce around defeated ideologies, but it tends to take a couple generations for it to build to a critical mass; atavism is a powerful force, especially when tied to a "lost" cultural or political ancestral identity.
Edit: NK is the most obvious exception here, and I don't know that much about it. I know most of the foreign policy wonks I know were surprised that there was not a coup during the transition from Il to Un, so it's possible we're seeing something new (or perhaps
dynastically old) there I suppose, but I think it much more likely it's just taking a little longer there due to the chokehold on media access.
The original trilogy was too vague to really say anything about how the canonical empire would have fallen, and the expanded universe, while better than anything Disney has made, is still a completely schizophrenic mess.
If I had to make a guess, I'd say that there was still significant continuity between the Republic and the Empire and that most viewed it as a simple transition from one to the other and back. Think Rome having a temporary dictator and then going back to the Republic. The difference being that there were no equally popular and powerful successors to take power in the Empire like Rome had after Caesar. Rome didn't just blindly acknowledge successors, you had to be effectively democratically "confirmed" by being popular/feared at some level with all the military/aristocrats/people of Rome or else you were either getting assassinated or end up fighting a civil war for power that you'd lose. Obviously the Empire didn't have someone to meet these requirements. Maybe Vader could have. But he also wasn't really a politician, so I'm not sure if he'd fare well. Rome was kind of unique in that politicians also served as provincial administrators of large portions of the empire along with serving as Generals, which allowed them to amass both a lot of experience and a lot of influence and support. To effectively take charge of the dying Empire you'd really need a similarly multifaceted person.
The Empire only lasted for ~23 years and the Senate was still in operation there for ~20 of those years. There's not really time to build up the Empire as a significantly distinct ideological force I'd say. Additionally, while the defining trait of the Empire is "we're the bad guys and will smash down dissent", they justified this based on the fact that the Clone Wars itself was bad enough, no one wanted a repeat, and the Republic was already acting fairly ruthless then anyway. It was never a from the ground up ideology that was promulgated like "survival of the fittest" or "the strong should rule". Yes I get that that's what the Sith are like but AFAIK the Empire didn't order that school curricula be turned into Sith doctrinal teachings. Nor is it likely that the Empire ever even could exert that kind of control, after all it couldn't even effectively patrol the galaxy and had to rely on fear to keep planets in line. For the majority of people who were just living their lives in the outskirts of the Empire its death was probably just a notification that the galactic mailbox that you write taxes to was changed.
My dude, I am a lifelong Star Wars nerd (well, used to be, now I'm old and Disney's ravaged the franchise), and at one point as a teenager I could have given you indices both alphabetical and chronological of all major players, planets, and events in the EU, so take it from me when I say you are seriously overthinking this shit; the Empire are just a very basic brushstrokes version of Nazism; basically the only thing that is ever revealed about their ideology in the original films is that they believe in racial purity, cult of personality, and strict chain of command. They're not meant to be realistic or intelligent, they're meant to be big, bombastic, moustache-twirling* villains. That's it. It's a George Lucas movie, there's no room for subtlety there.
*Without the actual moustaches... filthy things.
