> Easy fix, wait for the next billing, contact the bank explaining what happened, and block that and future debits

You'd also want to mail a letter to Google documenting that you're cancelling your subscription. Cancelling a payment method alone doesn't void a contract.

I doubt Google would do this. But there are plenty of trashy litigation-finance shops that buy up these abandoned contracts for pennies on the dollar and then try to collect. Even if you never give them any money, it would trash your credit for a while.