Hey @DanielCHood,
If your customer cancels their service you can go ahead and remove the subscription with DELETE account_activity/webhooks/subscriptions.
If you’re customer revokes access to your app, the subscription will be in place, however you would no longer receive webhook events for that user. The webhook service checks permissions before events are sent to your app’s webhook.
If you would like just check what the user’s status is, you can hit GET account_activity/webhooks/subscriptions or just hit something like verify_credentials to check if the access tokens are still active.