When testing Expiration policy settings for Teams in April this year, one of my customers noticed that although the policy successfully deleted the O365 Group and the associated SharePoint site/Documents (this takes approximately 24 hours), the Team and Channel were still present within the Teams application (both the Desktop client and the web version).
Further testing by manually deleting a Team via O365 group exhibited similar issues. If however the Team was deleted from within the Teams application everything worked as expected.
To confirm that this behaviour was seen across the board, I ran tests myself on my own tenant. Everything behaved identically.
As a result of the testing, the issue was raised with Microsoft, who advised me on 11th May 2018 that a fix had been deployed to resolve the problem, so moving forward, deleting an O365 Group will delete all of the Teams items associated with it.
For the remnants we had left behind, if the group had an owner assigned to it, then the owner could sign into the Teams app and delete the Team, which then removed the remaining items.
This has however left us with one Team where the O365 group was deleted via the Expiration policy. The team in question does not have any owners, so the users who are members do not have the option to delete the Team, only “remove” themselves from it.
At present I am waiting updates from Microsoft to see if there is a way to remove the Team. Will update this post when I know the outcome.