These coins are yours and yours alone from now on. Coins are also not monitored further (unless you decide to keep them in your Circle account - Which is unadvised anyway).
Sure, they couldn't do anything about the coins that you already transferred to a wallet that only you control, but they sure could lockup any bitcoins that you still had in your Coinbase account or just lock you out so that you couldn't buy anymore from them. Also, I'm pretty sure that the KYC laws require them to track your coins to some extent. They can follow them on the blockchain, it's all public.