I had the same thing. This is a copy/paste from what I posted on the livestream forum:
''At the Christmas party, I was killed by a pigmen that was spawned in a 'safe zone' and lost 34 diamond ore, and 31 diamonds, along with a lot of other stuff. I'm a little upset, if a mod or admin could help me out, it would be greatly appreciated.''
Now with that said, I just wanted to say that I feel compensation is fair in this case because I felt that the event was safe like spawn and towns are safe. I assumed that mobs were turned off, but they weren't. Sorry for your time.
Thanks,
Fish_James