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. Once the period elapses, Teams permanently removes the conversations and they become irrecoverable.
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). Teams doesn’t delete a document library when the Team is deleted.