Deleting an Office 365 Group Deletes your Yammer Group
Even if the Yammer Group was created first... So yeah, don't delete O365 Groups unless you want everything gone. If you need to recover: ##Do this off Network with regular powershell opened as Administrator Import-Module AzureADPreview Connect-AzureAD Get-AzureADMSDeletedGroup | Out-GridView Restore-AzureADMSDeletedDirectoryObject –Id xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Get-AzureADGroup –ObjectId xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Update - 08/12/2017 Microsoft are rolling this restore functionality into Exchange Online over the next month or two, so you wont need the script above soon: