"No Sith remains. And the lone Jedi that exists--the son of Anakin Skywalker--possesses an untouchable soul. At least for now. We must instead move towards the dark side. Palpatine felt that the universe beyond the edges of our map was where his power came from. Over the many years he, with our aid, sent men and women beyond known space. They built labs and communication stations on distant moons, asteroids, out there in the wilds. We must follow them. Retreat from the Galaxy. Go out beyond the veil of stars. We must seek the source of the dark side like a man looking for a wellspring of water."
Tashu's story ultimately leads to him getting captured by the New Republic, so I doubt he'll ever get the chance to see whatever the Emperor was doing out there. Mothma is Chancellor. Immediately moves to relinquish Palpatine's emergency powers and "demilitarize our government so galactic war cannot happen like this again." Plans to cut military by 90% when they are able to confirm an end to the war. She wants to help fund smaller militarized operations against the Empire forces. She has some advisors that agree with this line of thinking, but others that think this will lead to a series of smaller civil wars
There's a Tatooine interlude. They mention that there is still a power vacuum from Jabba's death.
In it, a guy named Adwin Charu (working for the red key company) goes on a Jawa Sandcrawler looking for high quality goods for his employer, not the trash they sell to just anybody. Meets a guy named Cobb Vanth, seems to have local knowledge. Cobb helps negotiate with the Jawas to show Adwin the rare goods. Amongst the rare goods are Hutt artifacts, parts of a sail barge, all burnt, twisted, and wrecked.
Also amongst the rare goods is a box. Adwin opens it, and it contains a full set of Mandalorian armor, "pitted and pocked as if with some kind of acid. Been through hell and back." Cobb claims it for himself, saying he is a newly appointed lawman. Cobb shoots Adwin and tells him to tell his boss to leave the sector or come after him and his "new--well, new to me--suit of armor." He leaves.
Oh yeah I forgot, there are Palpatine decoys being propped up by the Empire to convince people (in the capital and presumably elsewhere) that the Emperor is still alive, but it's not really fooling everybody.
There are references to Dexter Jettster and General Grievous. Also, one of the Interludes is about Dengar.
A Kubaz named Ooblamon is selling a red lightsaber in a trashed tenement in Taris. In the room is graffiti, and the author mentions a stencil of Vader's helmet with a phrase beneath it reading "VADER LIVES."
Three people try to by the lightsaber. A pale girl, and two in black robes. Faces concealed.
He asks who they are, she says "We are adherents. Acolytes of the Beyond."
He asks if they are dark side fanatics or just kids who want toys. She tell him to "judge us not, thief."
He warns them not to try to kill him once they get the saber. She says "we are not violent. Not yet."
He asks what they plan to do with it, she says "we will destroy it, so that it can be returned to its master in death." When they leave, the merchant's assistant asks if that was really Vader's saber, and he responds with a "who knows, who cares?"
There is an interlude featuring Han and Chewie on the Falcon. They are going on a low profile mission for the rebellion. It says that Han misses Luke, Leia, and even Lando, but it doesn't really touch on his relationship with any of them beyond that. Leia is only in the book in the form of a holovid speech towards the beginning of the book. Luke is NOT in the book. He is only mentioned, and some Imperial refers to him as the Rebellion's "golden boy"
Also worth mentioning, Han gets a message from a non-Alliance contact, Imra, that Kashyyyk (which is still in Empire control) has an opening that could be exploited to liberate the planet. It seems Imra wants Han and Chewie to help (with a team of other smugglers, mercenaries, and formerly enslaved Wookiees) liberate Kashyyyk, and they DON'T want the help of the New Republic.
Han agrees and goes off with Chewie to do this.
Wedge survives.
There's a very small group of Imperial leadership on Akiva. Admiral Sloane, who has command of what she claims is the last Super Star Destroyer. Moff Pandion (self proclaimed Grand Moff), who thinks there needs to be a strong, centralized emperor. The Satrap of the planet, who is a regional governor with little power. Arsin Crassus, a banker/slaver who helped fund the empire. And Tashu, the former adviser to Palpatine that I mention elsewhere.
At the end, it's revealed that Sloane (the only one of that batch to make it out of the Akiva conflict that the book covers) was reporting to a greater imperial Admiral, waiting deep in space. It's implied that he wanted the situation to go badly so that he could eliminate any competitors for power, and also see if Sloane was a capable admiral. I can't remember right now if he's mentioned earlier in the book, but I'll check tomorrow. Also I couldn't see if he was blue

EDIT: I just checked earlier in the book. Apparently this is the "fleet admiral." Sloane lies to the other imperials early in the book about him being dead and her assuming command of his ships. They spoke of him highly as an officer.
Cloud City has an interlude. It is still in imperial hands, but it seems like Lando and Lobot are behind the scenes in an underground effort to liberate the city. They aren't seen, just spoken of. There is nothing having to do with Luke/Anakin's saber being found there.
The penultimate interlude scene is on Jakku. It's really a desolate place. Sounds like it's just sand forever. Deals with characters we don't know.
One of them says "Not many folks FROM here. Most folks...just end up here. Jettisoned like so much worthless cargo. Dropped like waste."
He later says "you don't get more nowhere than here."
Nothing on the Knights of Ren. One of the Imperials that plays a small part in the main story is a guy named Tashu. He was an advisor to Palpatine. Seems like he is well versed in Sith history, and definitely thinks the remnants of the empire should embrace the dark side. No powers or anything, though.
It seems the political situation on the capital planet is that it still has Imperial presence, but it's weakening. Underground attacks and mass riots have been undermining imperial presence there.
Corwin shows up on Jakku at a bar in an interlude chapter. He came to Jakku because he wanted to get as far from the fighting as he could. Seems like his family's dead and he's just trying to get away.
Somebody in the coruscant interlude mentions a secret passage or something behind Dex's Diner.
One of the protagonists has a vibroblade wielding modified battle droid fighting for him. He mentions that he programmed its combat from multiple sources, including "some cyborg general from the Clone Wars."
The book sort of culminates with a mass riot/rebellion of its citizens. The Satrap is overthrown, the empire flees, and it becomes the first planet in the Outer Rim to officially welcome the New Republic, setting an example for other outer rim planets.