Alright, so here's what we know so far. It's likely to not be GOOD to combine them, but not because kava + time + alcohol = liver damage, it's because alcohol + time + anything = liver damage. Alcohol is the liver toxic substance, not kava, and kava doesn't amplify any such hepatotoxicity from alcohol.
Will it kill you outright? There isn't any research that would support that. Does it harm your liver when combined? Believe it or not, there is no research that would indicate this being the case either.
Alcohol and kava shouldn't be combined for what is known as "pharmacodynamic" interactions, or interactions in the way the chemicals actually exert their effects. With kava and alcohol it could cause a dangerous level of sedation that could make a reasonably small amount of alcohol be overwhelmingly sedative to the point of effecting driving even at levels under what's considered "legal".
Also we suggest not combining the two due to histaminergic interactions. Kava can cause the release of histamines which your body normally deals with pretty quickly, however with some people adding alcohol to the mix can cause a niacin like flush, hives, and itching due to the overabundance of histamine from alcohol competing for sites of metabolization. In short it can cause a really uncomfortable reaction if consumed together or too closely in time together for some people. The risk of this happening seems to increase with the % alcohol that is consumed. Beer seems to cause fewer problems, however spirits can be a big culprit of the issue.