While commenting on the rumored new design for Stormtroopers in Star Wars Episode VII, I was surprised to see that I was one of the few people that thought the Galactic Empire would almost immediately crumble now that its two chief architects, Emperor Palpatine and Darth Vader, were dead.
Points about the military strength and organization of the Empire were brought up, and essentially that a state of that size and power would not just fall apart when the Emperor and Vader died.
Now while these points are valid, I never really considered them with regards to the Galactic Empire because I viewed Star Wars as a Space Fantasy, a tale of broadly drawn sides of good and evil, with good wizards and bad wizards fighting to shape the destiny of the galaxy. So it made sense to me that the Empire would crumble after the dark power that built it fell, because the Sith powers of the dark side were the foundation of the empire, more than the military and technological might of the empire. If asked I would have lumped in the Empire with places like Angband and Mordor, both of which immediately fell apart after the evil that ruled them was defeated, as opposed to states like the Romulan or Kree Empires, both also portrayed as villainous for much of their existence, but displaying differing facets in their actions that entities like the Empire and Mordor did not.
So that led me to wonder where to draw the line between Space Fantasy and Science Fiction. Like all attempts to categorize fiction, it's mostly in the eye of the beholder, but it presents an intriguing question of where we make the distinction between the "logic" expected in Science Fiction no matter how fantastic, and a traditional fantasy story, where clearly good squares off with clearly evil, guided by prophecies and magic swords and ends with a clear winner. Does Star Wars lose something if you change the Empire from manifestation of evil to an oppressive, powerful superstate?
Take Apokolips and the Jack Kirby's the Fourth World, long held by popular wisdom to have had more than a little influence on Star Wars.
Apokolips, despite the advanced technology it possesses, is ruled by a space god who is not just evil, he is the embodiment of the idea of evil. Like the Emperor was demonstrated to do in the Prequels, his mere presence twists and distorts everything around him. Apokolips is an extension of Darkseid, and exists as long as he exists. Even in Kingdom Come, which chronicled a possible future of the DC Universe and showed Darkseid's good guy son Orion ruling Apokolips, Orion was only able to do so by slowly turning into his hated father.
This demonstrates the corrupting power of Apokolips and its creator and mirrors the downfall of Sauron, the Nazgul and of course, Darth Vader. I don't think anyone would expect Parademons to start negotiating treaties with the Green Lanterns if Darkseid were to die, so why is the Empire expected to be different?
As with Apokolips, I think the fantasy themes embodied by the Empire are more important than the more realistic concerns that govern how other science fiction empires are portrayed with regards to Star Wars. And to have the empire exist long after the death of the Sith lords that created it misses an important part of Star Wars and the relationship between the Jedi, Sith, and the galaxy they reside in and institutions they built.
ETA: I hope this is not viewed as advocating rigid rules on what makes what kind of story. This is me engaging the various stories mentioned based on the work presented. Nothing is obviously set in stone, but I would expect an exceedingly good reason to have Orcs securing trade routes or Romulans trying to plunge the universe into darkness with magic rings.