Regarding Control Hub Cloud and the logs retention policy, here is what we know so far: 

1- Is there an audit log telling who deleted which pipelines?

- No, but Adam has created a repo (https://github.com/kunickiaj/action-streamsets-control-hub) we can use to automatically back up pipelines on every commit to a git repo. 

2- in Cloud, do we retain logs for groups (changes, erasing, etc.?)

- No, only audit logs are for user login / password change