When you create a site with a group, it's very hard to delete the site.
I think you have to fix this bug: when eliminate a SharePoint site, groups should be eliminated on cascade.
Once you delete the group in the Office admin center for instance the site will be deleted
As a professor at a large research university, I have been included on the group list of several organizations. There is, however, no way to delete the groups that are of no interest and simply clutter Outlook 365. Doing so should be a user's option, but the way Outlook is setup any group can list a user's name with no option of removing oneself from the group roster.
Deleting a Office 365 group by using Office 2016 Client does not delete the sharepoint resources and sync entries for this group. Why?