In your future history, you need to take account of this - 'Hawking radiation'. That mitigates against your long term scenario of a universe-gobbler. It's probably connected to the entropy of the black hole, and recall that entropy has also to do with the gradual degeneration of a structure.

Also more simply, look around the universe. There are some gigantic black holes with billions of solar mass, but they sit at the center of galaxies for instance, and suck up infalling matter while radiating all this electron/positron plasma. They don't grow and take over the universe. Anything further out than the critical radius just orbits the black hole as if it were any other mass. That is what David was trying to say, I think.

If our sun was compressed to a few miles diameter at the same mass, it would become a black hole. But the planets would still orbit it as they do now. It would suck in nearby matter, and perhaps grow, but clearly some sort of dynamic equilibrium is always reached with the surroundings. That's observation, not speculation.

And remember the universe is actually expanding, at an accelerating rate - hardly the scenario for it to be sucked into the gurgler.