Working memory on a current task could be distorted, but I cannot find a reason to suggest sudden loss of electrical information would permanently alter short or long term memory.
Hopefully a neuroscientist can answer with a more electro-chemical oriented answer, but fundamentally I think the experts aren't sure what a memory actually is (there are only a handful of theories each that are understudied or flawed). This is also a fairly hypothetically question. Baring these points in mind, treat not only this, but all answers skeptically and take with a pinch of salt!
A recent review by Baudry et al covers the modern biochemical view on long-term potentiation (LTP) of the hippocampus that is probably responsible for things like learning and memory. It is a complex protein formation involving BDNF, calpain, and synaptic modifications. If hypothetically you became 'brain dead' for a moment, this way of looking at memory probably wouldn't take a hit.
Something I have less of a grasp on is Richard Semon's Engram, but was more heavily studied by Richard Thompson. Even the most modern studies describe this kind of brain mapping as chemical and cellular rather than electrical. So again perhaps nothing other than the unstored would be lost.
Working Memory loss
This rather technical article discusses primate prefrontal cortex neurone firing as a persistent stream needed for a "working memory". I am out of my depth here, but it seems like some "forming" memories may be lost if there was momentary activity loss, but I don't see why the underlying biochemical state that cause this effect would be lost, so very little information would be directly lost.
Memory loss. Diseases that cause memory loss involve tissue and protein changes along with other physiological changes. Memory loss induced by trauma is likely caused by swelling where the neurones are damaged by swelling or the trauma itself on a cellular level. It seems to be the case that the electrical information isn't the important factor to memory loss.
Note: I think memory would be lost indirectly, perhaps removed in a similar way as when you wake up from a dream or in cases of trauma. I am also ignoring that there would be a reasonable probability that this would induce seizure, stroke, or other bad health effects!