First "dead-out" leaves me puzzled

.....and sad.....I can't believe my strongest colony is no more. I went out to feed the bees for the first time(they had plenty stored away) and found one of my hives empty....empty...like my heart felt when I lifted the medium super of pollen and honey and found no bees... Gone. Was it the queen who was so strong just 2 weeks ago? Was it the workers who decided enough is enough? I only hope they all took off to some hollow tree somewhere, to live through winter. I realize the bees do not answer to me, but I was hoping for this colony to remain strong......guess I'll just hold off getting my 4th hive till 2013. On a brighter note, Merry Christmas y'all. Bee thankful, Kb