CB Auto Actions, the latest release now includes CBSubs triggers in the dropdown. Example configuration as follows.
Trigger: onCPayUserStateChange
Conditional 1: [var3] Equal To PLAN_ID_HERE
Conditional 2: [var2] Equal To A
Now use whatever action you want (for example the usergroup action). var2 is the subscription status, so you can reverse the usergroups by checking that it's not equal to A, which is active. var3 is just the plan id, which you match against so it only applies to a certain plan.
This basically gives you the full power of CB Auto Actions combined with CBSubs. The above trigger is the same one we use in many of the integrations (can be reviewed in CBSubs 3.0 GPL).