Any Member of a Team Can Delete a Channel
By default, any member of a team can delete a channel. The sole restriction is the General channel, which cannot be removed. If you want to stop team members deleting channels, edit the team settings and uncheck the box to “allow members to delete and restore channels.”
When a channel is deleted, Teams hides the messages that make up channel conversations and starts a 21-day countdown. During this period, a team owner (or a member, if allowed), can restore the channel. Once the period elapses, Teams permanently removes the conversations and they become irrecoverable. However, Teams leaves any data accessed through the channel tabs alone. Although this might surprise some, “Do No Evil” is the right approach.
SharePoint Folders and Teams Channels
Every channel in a team has a folder in the document library in the SharePoint Online site created by Office 365 when it provisions the Office 365 group belonging to a new team. When you create a new channel in a team, Teams creates a folder with the same name in the document library to store files uploaded to the channel. The folder is accessed through the Files tab in the channel (or the SharePoint browser interface). Because Teams creates a folder when it creates a channel, you might think that Teams should remove the channel folder from SharePoint when a channel is deleted. However, this doesn’t happen.
The fundamental reason why the folder is left is that Teams and SharePoint Online have a close but loose relationship. Creating a folder does no harm, but deleting a folder can be very destructive. Teams stores files in the folder, but other applications can store files there too, and users are able to access the folder to work with its content through the SharePoint browser interface. It’s therefore possible that some extra content might be uploaded to the folder that isn’t associated with channel conversations. If Teams deleted the folder along with channel conversations, it would remove that information too. As the support article for the topic notes, the folder also holds some OneNote sections that you might want to keep.
Retention Might Prevent Deletion
Another reason is that Teams cannot assume that it can remove content from SharePoint. The site, document library, or individual files might come within the scope of an Office 365 retention policy, or individual files might be assigned a retention label. In either case, the presence of retention settings can prevent the removal of SharePoint content.
Examine All Channel Tabs
If you want to clean up all traces of a channel, you must first remove it from Teams (and wait for the 21-day countdown to finish) and then remove any other content associated with the channel. The most obvious content is in SharePoint, but there might be other content linked to tabs like plans, forms, and so on. For this reason, before you delete a channel, check out the tabs to understand what content is linked to the channel and then decide what should be removed and when.
For more information about Teams, see Chapter 13 of the Office 365 for IT Pros eBook. Office 365 retention policies and labels are explained in Chapter 19.