With that being said, CM did not promise (to my knowledge) to delete old private keys. But also, I think it is unlikely that CM had 6 TB worth of private keys stored on their servers.
There would have to be around 200 billion private keys on file in order for it to take up 6TB, which is an order of magnitude larger than the number of active addresses.
I suspect that it's mostly other data, eg: Running a full node will take half a terabyte, and metadata related to the chips; I wouldn't be surprised if that was a few TB as well.
If charges were filed against DS, the reason law enforcement would have waited 6 years would be to not tip off the operator that law enforcement was coming after them.
Now hey. Didn't Hhampuz manage the Bitblender campaign which was also seized abruptly?
Relax, nothing is going to happen to them.