I myself have relied on “Activity Alerts” in the Security & Compliance Center and it has worked well. As soon as someone deletes, for example, a Team or a Planner, a notification is sent to a team channel in my Governance Center and then I know that it might be something I should look into.
In the article “Reporting Team Deletion Events to Office 365 Administrators” by Tony Redmond, he highlights that Activity alerts and Activity Policies may have some shortcomings. This is nothing I have experienced (yet) but his alternative solution, based on PowerShell, described in the article is clearly interesting so it is worth testing.
In his sequel “Reporting Office 365 Group Deletions” he also writes about how this works for Groups that are deleted by a “Group Expiration Policy“. This is also important to know if you want to be sure to have control over one’s Office 365 Groups.
Here You can read more about how to “Plan for governance in Office 365 Groups”
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