How to kill bees

My neurotic bees have died. Over the past few weeks the cluster of bees got smaller and smaller until there were insufficient bees to keep the meagre brood warm, and the colony faded away.
It was always an unsatisfactory colony; constantly busy but unproductive. Last summer they produced a new queen and I was hopeful that their characteristics would change, but the neurotic behaviour continued. I could never find the new queen until a few weeks ago when I found her in the diminishing cluster. What a poor specimen she turned out to be - dark and skinny and not much bigger than a worker. "No wonder the bees were anxious" I thought.
But a poor queen does not explain why this colony died, only why it never flourished. The prolonged winter didn't help. Each cold day that passed meant fewer winter bees to keep the brood warm and no fresh pollen coming in to keep it fed.
And that shook swarm weakened the colony further - but shouldn't have killed it because my other colony is doing fine. So what killed this colony?
Well I'd like to say all of the above, but I'd be making excuses because .... I killed the colony.
It was a cock-up rather than a conspiracy. When checking the bees a few weeks ago the solid crownboard that sits on top of the hive got switched with the crownboard with a hole in it to allow the bees access to the feeder. The upshot was that for almost 2 weeks the bees weren't fed.
I'm not best pleased with myself and I realise now why those bees were neurotic - they didn't trust me, and who can blame them.