According to Wookieepedia using Star Wars: The Last Jedi: Expanded Edition as a reference seems to have embellished a bit beyond what we find the actual source:
In spite of significant damage to the ship, it nonetheless remained functional.
Regardless, the flagship was later deemed to be a lost cause by the First Order, evacuated and scuttled.
Here is what we can verify from Star Wars: The Last Jedi: Expanded Edition:
The ship or at least parts of it were still working:
The Raddus had hit left of center, sparing the section of the Mega-Destroyer that housed the overbridge and the throne room. Which was fortunate for Hux—as the bridge descended into chaos, he had hurried to the turbolift connecting it with the Supreme Leader’s sanctum. It wasn’t until after he’d stepped into the lift and used his code cylinder to access the throne room that he realized it might not work.
He looked around frantically, gripped by the fear that he’d consigned himself to an ignominious end—the architect of the First Order’s military domination spending his last moments trapped in a turbolift. But the lift descended so smoothly, Hux had no idea anything was wrong.
General Hux was not too worried about its destruction (and didn't even think about repairs) though:
The First Order’s flagship—which was also its mobile capital, its greatest shipyard, its best research-and-development facility, and so much more besides—was doomed. Yet the Resistance had been reduced to a pathetic handful of ships trapped on a backwater world. And the New Republic was no closer to resurrection. The imminent end of the Supremacy would change surprisingly little about the balance of power in the galaxy
And it does seems that ship was beyond repair and failing quickly:
The throne room lurched sickeningly around them. Hux knew what that meant—the complex system of inertial dampeners and acceleration compensators that protected the core decks of the Supremacy was failing. They had to hurry. But Kylo was confused. He braced himself, staring out in disbelief at the mangled half of the flagship and the wrecked Star Destroyers beyond it.
This is the last mention of the Supremacy in the book, so it seems that the quote from Wookieepedia probably happens in a very short span...