A large spacecraft is powered by a massive fusion reactor - in essence, a miniature star. This star is surrounded by a dyson sphere at the center of the spacecraft.
The star's radius is about 5 times as small as that of our Moon at 350km, and assuming it would have twice the mean density as that of our Sun at 2820 kg/m³, it would have a mass of about 500 quintillion kg, an infinitesimal fraction of our Sun's mass, and about 0.008% of Earth's mass.
Handwavium technology is used to exert upon the star the enormous pressure it requires to sustain fusion, and it also prevents such silly things as radiation and immense heat from swallowing up the spacecraft and its inhabitants. How this handwavium works and why the builders of the spacecraft even need a fusion reactor with such ridiculously powerful technology at hand is irrelevant to the question.
The handwavium suddenly stops working and the miniature star is now exposed to the harsh realities of the laws of physics. What would happen next?
Would the star simply swallow up the spacecraft and then disperse into a harmless cloud of hydrogen?
Would it do the same thing natural stars do when they can no longer sustain fusion and go nova, ruining the day of anything within a couple AU?