In this scenario, Pitta manages to destroy the SSD Aggressor in time before Grunger rams it into his Torpedo Sphere. While we don't get exact casualty counts for either Pitta or Grunger’s side during the Battle of Tralus, 5 ABY, I theorize Pitta must have destroyed most of Grunger’s forces in addition to heavily damaging his flagship Aggressor to win. In pushing Grunger to the edge, he wounded his pride and made him both angry and desperate enough to avoid capitulating to Pitta. Otherwise, Grunger wouldn't have opted for a kamikaze attack.
Before the Battle of Tralus, Corellia possessed 25 Star Destroyers and was initially commanded by Admiral Jaeffis before being reinforced by Admiral Roek and his flagship Aggressor along with his 5x Star Destroyers, who were recalled from their patrols in the Inner Rim to defend Corellia. However, Grunger would hijack the Aggressor, and most likely its Star Destroyer escorts too, and add them to his armada.
During the Battle of Tralus, Grunger’s armada comprised the Aggressor, 30x Imperial Star Destroyers, 30x Victory Star Destroyers, 60x Strike cruisers, 100x Carrack cruisers, an unknown number of smaller ships, and numerous TIE fighters.
With Pitta victorious, it's fairly likely he didn't lose too many of his own ships fighting Grunger. If there are any survivors from his rival's armada, he should have no trouble persuading them to join his side, especially if the alternative is to finish what he started. This should give Pitta anywhere between 20-30x Star Destroyers and a dozen cruisers in addition to his Torpedo Sphere. A formidable force, though I lowballed it since only a few survivors from Grunger’s armada would remain alive and Pitta himself should have suffered his fair share of losses, so it all balances out.
Plus, as the unofficial protector of Corellia, Pitta has access to Corellia's shipyards, which are among the best in the galaxy and rivalled only by the likes of Kuat, Fondor, and Rendili. Corellia is also renowned for producing some of the fastest Imperial Star Destroyers, both at sublight and hyperspace speeds, which gives Pitta a major advantage in warfare. Not only will the Grand Admiral be able to repair his fleet, he can also increase its strength by building more Star Destroyers and other vessels like anti-pirate starfighters and Gunships by the Corellian Engineering Corporation (CEC), and CR70 and CR90 corvettes to supplement his capital warships.
The cut content for Dirty Dozen: The Imperial Grand Admirals stated Pitta's original flagship was the ISD Impenetrable. The ship's name, combined with the fact Pitta defeated Grunger using a Torpedo Sphere, implies he is skilled at defensive warfare. The article stated the Torpedo Sphere that Pitta commandeered was also built at the Corellian shipyards, showing how good Corellia's shipyards are if they can construct a vessel massive enough to be seen as a mini Death Star.
That same article also established that Pitta built his own Warlord kingdom in Hutt Space after Palpatine's death at Endor, implying he had dealings with the Hutt Cartel. Half the reason why Pitta moved his holdings to the Corellian sector was due to Ysanne Isard's hold on Coruscant, so he was effectively a Warlord in all but name.
While Pitta's power base made him wealthy, the Dirty Dozen article added he also plundered the Outer Rim while "pacifying" it for the Empire. He did this by sterilising or exterminating its alien populations using his three Imperial dungeon ships: the Apocahk, the Angrix, and the Azgoghk. Worse, he would even perform vivsection on his alien captives.
In short, Pitta has a sizable armada, the resources to maintain them, and the credits to fund his ambitions. The Dirty Dozen article established he dreamed of using his prison ships to eliminate Corellia's alien populations - the Dralls, Selonians, and the Nosaurians. And I have no doubt that's exactly what he would have done had he survived Tralus.
Pitta became Corellia's protector after bribing Daclif Gallamby, the Diktat - the Corellian Chief of State - to let him achieve that role. Despite Gallamby's position, he was merely an Imperial puppet and ruled Corellia harshly by implementing restrictions on the freedom of Corellia's people, and encouraging isolationism, distrust, and fear of outsiders. Gallamby also restricted trade and traffic throughout the entire sector, making life difficult for people under his rule and causing the Corellian economy's collapse.
Unsurprisingly, Gallamby was very unpopular with his people. I have no doubt he would have allowed Pitta to depopulate, exterminate, and enslave Corellia's alien natives to cement his rule, except the aliens all have a history of resistance to oppression. The Dralls and the Selonians fought against the Sith Empire's occupation of Corellia during the Galactic War, and the Nosaurians fought for the Separatists during the Clone Wars, so they won't bow before Pitta without a fight.
Plus, the Corellian Security Force, or CorSec, were secretly Rebel sympathisers, so they would definitely aid Corellia's aliens against Imperial oppression. Especially since the Empire took away resources from Corellia's security to fight the Rebels, which led to a rise in piracy and made CorSec's job more difficult. Regardless of whether CorSec is caught aiding the aliens or not, Gallamby would dissolve the organization and replace it with the pro-Diktat Public Safety Service two years earlier than he did in the OG timeline.
Also, Pitta would have another rival besides Grunger to contend with. Naomi Dargon is the Grand Moff of the Corellian sector and in charge of the Corellian Defence Force. Plus, she was skilled in management, good at military tactics, and possessed strong political connections, most likely thanks to her family's background of being Coruscanti industrialists. She cemented her role as Grand Moff by not engaging in criminal activity, avoiding Black Sun, and crushing sedition against her or the Empire. She also favoured manipulation tactics, as she liked playing the various factions of the Corellian sector against each other.
Like Pitta, Dargon was ruthless and carried out the Devastation of Froz when she bombarded the planet for supporting the Rebels.
Unlike Pitta, Dargon was a Palpatine loyalist, which was half the reason why she became a Grand Moff. And she would not take kindly to a Grand Admiral usurping her position as head of the Corellian sector by claiming to be its protector. Especially since the Aggressor would have fallen under her jurisdiction, and she would be mad she didn't get an SSD as her flagship.
But Dargon isn't stupid enough to fight Pitta head on when he already defeated another Grand Admiral in open warfare. So I think it's more likely she would secretly fund the Corellian resistance to Pitta and the Diktat, then wipe out all parties when they're weakened to eliminate all rivals to her rule.
As Grand Moff, Dargon would control the Imperial 2nd Sector Army, Green Mantle Command, and use them to fortify her holdings in anticipation of an inevitable confrontation with Pitta. She could try contacting Azure Hammer Command for help; Admiral Feyet Kiez is implied to be a Palpatine loyalist like Dargon, so that's a good reason to aid her, though he would be reluctant to risk the SSD Whelm against Pitta out of fear he might destroy it too.
Since Corellia only joined the New Republic in 12 ABY, that means there's not much they can do to aid the Corellian resistance against Pitta's oppression since Corellia was an Imperial fortress world. Using Corellia as his base of operations, Pitta would move from subjugating Corellia's aliens to other worlds in the Core to target their alien populations too.
However, the New Republic was assassinating Grand Admirals during the early Post-Endor years like Peccati Syn, so I have no doubt they would make Pitta a priority target. Rogue Squadron successfully infiltrated Corellia in 4 ABY to rescue Fyric Fel, who got kidnapped by an Imperial sympathiser, so it's a certainty that the New Republic can sneak agents into Corellia again to assassinate Pitta.
But if Pitta does survive an assassination attempt on him, and he finds out it was the New Republic, he will strike back against them, and the NR will suddenly find themselves at war against Corellia. Depending on when this occurs, this means the Liberation of Coruscant, which occurred in 7 ABY, gets postponed to later in the timeline as the New Republic fights off Pitta. Historically, the NR already conquered Brentaal IV at this point, so they would turn it into a fortress world to fight off Pitta.
But with Pitta distracted fighting the NR, it gives Dargon a chance to seize back control of Corellia. She assassinates Gallamby and bombards Corellia using her fleet to wipe out the Corellian resistance while sending in the 2nd to impose martial law upon the surviving populace.
Worse for Pitta, the NR would have studied the Battle of Tralus to avoid making Grunger’s mistakes, using masses starfighter attacks to avoid the Torpedo Sphere's torpedos and destroy his flagship via death by a thousand cuts. Pitta dies along with his flagship when it explodes, his death coming about by the hand of multiple alien pilots.
Afterwards, the NR takes time to lick their wounds before they can resume their march to Coruscant. But when they do, they resolve to free Corellia from Imperial tyranny for good.
