Anybody with the power to harness wormholes, therefore harness the power of gravity, is not something I think we could fight.
They'd harness the power of space and time.
Also, don't worry about that. Chances are if we're all going to die, it'll be because of tidal forces stemming from the sheer gravitational pull of the Black Hole, or because of the mass amounts of radiation already likely burning up our atmosphere and poisoning us.
If we do survive through all that somehow though, then we can manipulate plants and food sources to work without sunlight.