I was curious. My synthesist was just killed by wights. Their negative levels got me. But, afterwards, I remembered the FAQ stating that ability damage was done to the eidolon, not the summoner, when it was active. So, would the negative levels just affect the eidolon, killing/banishing it when the negative levels equaled it's hit die? It seems like it would work the same as ability damage to me.. I don't think this will save my character, though it might, since once he died, the game kinda stopped for the night. But even if it doesn't, I'm curious, and if it is the case, this might need to be added to the FAQ.