Mustrum_Ridcully
Hero
Ignoring the novels (as the new movie does), the most likely "What happens after The Emperor was killed?" scenario is something like Original Traveller's* "Imperial Civil War" adventure module: a half-dozen large successor states (one is the New Republic and the audience is encouraged to root for it) plus countless de facto independent worlds and multiple petty states. Several Imperial Admirals / Generals can build a space to rule; Hutt space is a Thing again. Some other pre-Old Republic nations / races may have reasserted themselves as independent or effectively autonomous.
I wish the movie HAD used the novels, since Grand Admiral Thrawn was a natural BBEG - his master plan has aspects both glorious and nefarious. Good-hearted men can aid him in his endeavors, accomplishing shared tactical goals, even if they dislike his final purpose. He is not a Force-adept, so he's not a complete Palpatine clone. He's trying to emplace himself as somebody else's Grand Vizier (but he hasn't found somebody to be The Boss) rather than rule all in his own name.
* You can now make a good guess at my age.
Thrawn seemed to fit really well into the Star Wars universe, but with a distinctively different approach to strategy or people skills.
Thrawn used guile and trickery, and while he did rely on "super weapons" to some extent, he used them in surprising and unpredictable ways. He handled defeats a lot better, and had contingencies.
Taht is what mostly disappointed me about the new movie - the starkiller just seems doing more of the same.
That said,we'll see how things evolved. If Episode IX features a incomplete starkiller... A nice touch was that Snokes didn't rage or anything whe he heard the starkiller weapon was destroyed - he just calmly ordered evacuation and retrieval of his pupil.