When you scroll all the way down, above the Delete this group section you can find the Unsubscribe section.
This function is used only to remove your own user from the group and thus will not affect anything related to the group and its data at all. It will only remove this group from the list of groups available to you, and consequently, revoke your access to it completely.
By clicking on Unsubscribe, a window will appear in which you will need to type the name of the group you are currently managing and click on Confirm. Consider carefully when proceeding as this action will remove you from this group, and in case you do not have any more groups besides this one, you will be removed from the platform entirely.