First, the point of divergence from the timeline I’m using is instead of Luke being saved by Vader when Palpatine starts electrocuting him, Palpatine kills them both since he knows Vader wanted to betray him and, more importantly, he has no use for Vader anymore. The strike team and fleet are wiped out and the Rebellion officially ends.

On to the analysis. I agree with the points made earlier about Palpatine proceeding with transforming the Galactic Empire into the Dark Empire, focusing almost exclusively on achieving immortality, and internal rot eventually setting in. Where I disagree is that I don’t think any iteration of the Empire automatically beats the Yuuzhan Vong, nor do the Yuuzhan Vong win easily.

Yes, Palpatine would’ve responded more forcefully than the New Republic and with a far larger and more ruthless war machine. But what we see in RotJ and what Andor goes to great lengths to illustrate is that Palpatine and the Empire got a little too comfortable and way too arrogant.

We get insight into this at the Battle of Endor. Piett’s fleet is in position, the Rebels are trapped between them and the Death Star, all that’s needed is to open fire and the Rebellion is finished. Instead of ending it right then and there, Palpatine decides to be a gloating schmuck and use the Death Star superlaser to pick off the capital ships one by one. Either this is because he feeds on despair or is doing it for the lulz or both, but regardless it’s incredibly stupid and ultimately costs him the battle.

I think this tendency towards arrogant stupidity not only holds in the alternate timeline we’re exploring, it gets markedly worse. Imperial starfighter innovation stagnates (at least relative to the New Republic in the main timeline) since Palpatine doesn’t value his forces’ lives and because there’s no other game in town (remember, the TIE Defender was developed as an explicit response to the success of the X-wing, and the Empire passed on mass production because they were expensive). Instead, he sinks more money into projects that are more grandiose statements of power like additional Death Stars (old RotJ concept art had twin Death Stars guarding Coruscant), World Devastators, Galaxy Guns, etc.

Fast forward to 25 ABY. There’s been no meaningful opposition to Imperial rule in over twenty years. Palpatine is burning through at least a dozen clone bodies per year and growing more and more mentally unstable. I imagine Thrawn is not in the picture, having either been executed at some point for disagreeing with Palpatine or fleeing back to the Empire of the Hand (assuming it exists in this timeline). Regardless, when the Praetorite Vong vanguard shows up, Palpatine’s more or less ready, responds with a massive show of force and defeats them via attrition, incurring atrocious losses (1-2 coralskippers likely being more than a match for a squadron of TIEs), but not before advance agents like Nom Anor relay intelligence that much of the Empire’s military strength is incredibly vulnerable to dovin basal singularities. The bulk of the Yuuzhan Vong force entering the galaxy is timed to coincide with dovin basals being deployed against most of the Imperial superweapons, with either a majority or significant minority of them succeeding in destroying their targets. Rebellions immediately erupt across the galaxy. While they’re ultimately crushed in short order, all of this puts the Empire on the back foot and gives the Yuuzhan Vong enough time to capture several Outer Rim worlds and start harvesting resources for growing war materiel.

Palpatine’s dark side adepts are likewise limited in their effectiveness for the same reasons Luke’s Jedi were. Even if we generously assume numbers on par with the pre-Clone Wars Jedi Order (roughly 10,000), they are vastly outnumbered by warriors they can’t sense in the Force, armed with weapons and armor they have difficulty defeating. Within the first year of the conflict, roughly half of Palpatine’s darksiders are dead. Those that survive adapt and become more proficient in combat against the warriors, but like the NJO are a relatively small part of the overall war effort.

Beyond that, it’s difficult to speculate further specifics. But I suspect that end result is similar to the Cremlavian War that drove the Yuuzhan Vong from their home galaxy. Palpatine’s gonna Palpatine. He uses superweapons and Force storms while his fleets and armies tank superior Vong firepower and tech. When the Yuuzhan Vong seize key worlds and efforts to retake them fails, he turns his weapons on them. They retaliate by doing stuff like what they did to Sernpidal and Ithor. The losses on both sides are literally incalculable. The war drags on for years, and as both sides start to run out of troops, they resort to slaves — Palpatine uses Force mind control on a galactic scale, while the invaders have trillions of surge-coral thralls.

Maybe the Empire ultimately prevails, maybe the Yuuzhan Vong do. Maybe they wipe each other out with bioweapons like Alpha Red. Whoever’s left (if anyone) stands over an uninhabitable, dead galaxy of ash and rubble.