Board Thread:Questions and Answers/@comment-115.73.154.178-20130911141214/@comment-131.194.164.107-20130912232845

If the whole guild loses (isn't able to defeat Virgo[Fallen] at that level), then the next time you find Virgo[Fallen], it'll be at a lower level. It doesn't matter if you keep losing or attacking until you have 0 spirit left. What matters is the end result.

In fact, with the way the event is set up, it's pretty much impossible to defeat a higher-level Virgo[Fallen] without losing most of the battles.