Our agency recently worked with a local company on handling some of their management overflow. It has recently come to my attention that the end client has terminated this relationship, and has now started running ads for the same domain and keywords on two accounts - one they had previously, and one that they established for this new account relationship.
I've already unlinked our MCC from their account that we were working under, but I figured I'd reach out to the community to see if there are any steps I should take to further protect our MCC if they get a policy violation strike in the future. This whole situation has been a set of firsts for us, so I appreciate any insight from the more experienced agencies here!
I don't think there's much more you can do to protect yourself. You removed the account from your MCC, so you don't have any more connection to this company/accounts. We have had approval/policy issues with individual accounts over the years, but that has never directly affected any other clients in our MCC. Maybe those issues have something to do with performance or specialization ranking, but if you've removed the account, then you shouldn't have anything to worry about.