I think the next thing he needs is to bring it to the meta section to get more suggestions or if he already send these sign message to the recovery email then he needs to wait to check if that address is confirmed he owns that account.
It's all already there. He created themes wherever it could be done.
https://bitcointalksearch.org/topic/possible-account-compromise-5410156
Another thing is that he will no longer be able to improve the situation with his loss.
I have no doubt that the deal was with a scammer, and if you just track how many accounts belonged to the "seller", then believing in his innocence is simply illogical. I showed the first accounts associated with the seller's account, and they have negative tags.
https://bitcointalksearch.org/topic/m.60767548
https://bitcointalksearch.org/topic/m.60767718