What has been shared by f1365 is not true as of 2019-10-23 You run Remove-SPOSiteGroup cmdlet to remove SharePoint Online group.
As of 2019-10-23 you cannot complete the following actions:
- Disconnect SharePoint Online from the group
- Change SharePoint Online connection from one group to another
- Connect SharePoint Online to an existing group
If you remove Office365 group which is connected to SharePoint Online site completely by running something like: Remove-AzureADGroup -ObjectId 50d28f25-b39d-4459-a05a-8257d28aef36 ;
Remove-AzureADMSDeletedDirectoryObject -Id 50d28f25-b39d-4459-a05a-8257d28aef36
You'll likely get 404 error when trying to open corresponding SharePoint Online site:
