There is a mind-bendingly massive black hole at the center of our galaxy, and our hyperdimensional idiot antagonist just dropped his wallet in it. He figures he'll just turn it off for a bit and fish it out, much to the chagrin of - well, everybody? I guess?
The assumptions -
- The event horizon is gone.
- Physics works, except for the bit about the event horizon being gone.
- The reason the event horizon is gone should amount to an application of energy, charge or force that overcame the gravitational force of the singularity.
- Once the event horizon 'opens', the idiot stops doing the thing.
- Whatever he did, he does not take measures to undo it directly.
I think it has to unleash a speed-of-causality wall of super-supernova proportions, like when a black hole evaporates below the mass limit. But that's the thing - this hole is so far above the limit, I'm pretty sure it'll burp (very, very loudly) and then immediately collapse again.
So assuming, for instance, he spun this black hole to an absurd angular momentum, what might the outcome be, for the black hole and for the galaxy it anchors? Can the black hole immediately reform, and start reincorporating the lost mass? Does the matter have to finish expanding first? Or is the situation so far out of bounds that the result cannot be approximated?