About the energy, unless we really go way out there and say energy conservation doesn't matter, I'm sure the Fog run out of "fuel" sometime, whatever they use. It just doesn't have to be within the next few centuries...
I quite doubt they're using anything as mundane as regular fusion power plants. While it would be a near infinite power source, it probably wouldn't output enough immediate energy, at least with reactors than can fit in these ships.
I just thought it might be something that exploits degeneracy pressure to manipulate gravitons or other exotic particles. Matter in a degenerate state have altered quantum energy states and is still otherwise 'regular' matter, it's not irreversible.