Notify the project followers whenever a "Deploy key" gets revoked
CircleCI projects are set up by clicking the "follow project" button on the CircleCI dashboard. What this does, is creating a new web hook and a new Deploy Key on the Github repository associated to that Github user that followed the project.
When a Github user leaves the Github organization or manually revokes the Deploy Key, the CircleCI builds start failing because they can't clone the repository; and this goes a bit unnoticed.
Ideally when a key is no longer valid (because it gets revoked, removed, or expires somehow) CircleCI would ping the project followers in any of these ways:
Send an email
Use slack/chrome webhooks to push notifications
Show a banner on any recently failed builds informing the keys were not valid.