I wished I found a flaw in your plot, because it is devastating for anyone's hope of ever getting stuck assets out of Gox.
But so far I didn't find any. Congrats, that all sounds quite reasonable to me.
Looking at the volume charts between mid 2011 and today, Gox may have gained about 200k-300k btc in total from fees.
That lines up well with about 800K btc missing, operating cost can probably be neglected in that calculation.
Keeping the keys for 1000000 btc on the server would not have been necessary. Once there was a substantial amount of btc on hot wallet addresses, they could have sent them to cold storage with one click, even if this was a paper wallet being locked in a bank safe.
What's left, at least for me, is to check for any confirmation of a $1000k steal on that day. We are looking for $1000k coins which mostly entered Gox during the weeks before and then were all spent more or less at once. The thief would have had to do the latter in order to prevent Gox from spending them first using a backup of the wallet, after the theft had been detected.
I wonder how plausible it is that the fact of such an amount of coins being stolen could be kept secret. But never verifying your wallets against the blockchain would certainly be helpful. In that context, the late detection of of double-spends due to TM is even plausible without introducing TM on purpose.
Thank you for the comments.
I agree that this process could have and should have been automated, but I also think that it's plausible that it wasn't:
1. Prior to the run-up from $1 - $30, I imagine that the amount of bitcoins on Gox was roughly constant. Mark never bothered to write code to automate this process since it was rarely needed, and the security was really designed to protect $100,000. Not $30,000,000. He
knew he should write code to do this as the price was climbing, but was just too busy from the explosion of business.
2. I assume that MtGox was flooded with bitcoins deposits in the days before the crash from $30 to $10. So it would make sense that the hot wallet would be very full. If indeed transfers to the cold wallet were not yet automated, then I think what I described is still plausible.