Microsoft 365 Groups and Teams that have no activity for a year or more, and whose owners do not respond to warning notices, are deleted. Any activity in the Group or Team from any member within thirty days of the owner receiving a deletion warning will reset the countdown timer to one year. Activity can include posting a comment, uploading a file, or clicking a reaction.

Group members will have thirty days to respond after the initial deletion warning to the group owner, but only group owners will receive the warning.

Some Groups and Teams have no owners, possibly due to their sole owner leaving the university. For these, notifications are sent to previously active members asking if they want to become the owner. If no one has, there will be no further notification before deletion, because the deletion notices are only sent to Group owners. This setup is determined by Microsoft's design of Microsoft 365 and cannot be altered. As a best practice, make sure your teams and groups always have at least two owners.
 
This mechanism is part of Microsoft 365 and intended to provide automatic cleanup of abandoned groups. Again, any activity at all in the Group or Team, such as posting, reacting, or uploading a file, will reset the time to be deleted to one year after the last activity occurs.
 
For more information about Group and Team deletion, see Cornell Microsoft 365 Content Retention and Deletion.