You may be unable to delete a delivery group from Web studio and PowerShell SDK, failing with the error "Database could not be contacted"

None.

It is caused by the MachineConfiguration linked to the Delivery Group. If you run following PowerShell cmd let, you may see the Uid value left in the MachineConfigurationUids as shown below:

Get-BrokerDesktopgroup -Name "<Name of the Delivery Group>"

MachineConfigurationNames                         : {<Machine Configuartion name>}
MachineConfigurationUids                             : {XX}

Please use following steps to remove or delete the Delivery Group:

1. Download the Remote PowerShell SDK
2. Install the SDK on any computer in your resource location except the Cloud Connector.
3. Add the Citrix snap-ins: asnp citrix*.
4. Execute the cmdlet, Get-XdAuthentication, it prompts you for Citrix Cloud authentication.
5. Run following PowerShell cmd let:

Get-BrokerMachineConfiguration -Uid <Value> | Remove-BrokerMachineConfiguration -DesktopGroup "<Name of the Delivery Group>"