https://www.bbc.com/news/science-environment-53235909 Sure, maybe it collapsed into a black hole without a supernova. Or dust is obscuring it. But my money's on Starkiller Base charging up for a shot to destroy the New Republic.
Well, one of the possible tell-tales for an advanced extraterrestrial civilization is unnatural changes to a star. Could be a K2 level civilization at work.
Actually, it might work that way. If the robots you have building the sphere are doubling the size of the sphere every day, once you hit the point where you had half the star covered, the next day, it'd be gone.
