Well, power failure isn't necessarily random. The way Lazurkri thought about gravity affecting materials inside the tanks does seem uncontrollable; I'd imagine that the kerbals' antimatter containment is advanced enough that they are able to store it safely (albeit with power usage, to keep particles from hitting the sides via magnetism) in their tanks already. If one does run out of power, the tank could explode with regards to the amount of antimatter inside. This is able to be prevented, just like one is able to prevent a spacecraft from crashing into Kerbin by adding parachutes. The explosions, however, would give antimatter a nice element of danger that is really lacking at the moment.