Am I the only one who's surprised that 1900 Bitcoin was stored in hot wallets?
I don't think it is really possible for a mixer to not store all their coin in their hot wallet. If CM used cold wallets, moving coin to/from the cold wallet really couldn't be done on-chain, otherwise, it would be clear which groups of addresses belong to CM. Also, CM's operational model effectively put all their coin on a hot wallet, regardless of the location of it's private keys due to the fact that CM had such a low threshold for someone to get a "chip", which is effectively an IOU from CM to their customers -- all that is needed is a browser session.
Keeping funds offline would have been possible: once in a while, when they run out of chips, users could only get a voucher until new chips were created. In the same way funded keys could have been kept offline.
I think the backup-scenario sounds logical: 7 GB of data including several snapshots which includes some of the used private keys. I'm now curious if there's anyone left with (older) chips that haven't been emptied. I checked the changes
here yesterday, I'll do the same to day to see if more keys got swept. If that happened, I assume it's their owner emptying them now.