You can permanently delete a Microsoft SharePoint Online Office 365 Group from your Azure Portal, but if you prefer to use PowerShell, here is an example.

	Install-Module -Name AzureAD 
	$tenantUrl = "https://{{yoursite}}-admin.sharepoint.com/" 
	$groupToDelete = "{{groupname}}" 
	Connect-SPOService -Url $tenantUrl 
	Write-Output "Connected to $tenantUrl" 
	Get-AzureADMSDeletedGroup $groupToDelete | Write-Output "Group $groupToDelete was found" 
	#Remove-AzureADMSDeletedDirectoryObject –Id $groupToDelete