Proxmox KVM virtual machine: Cannot delete due to missing storage

Today we encountered a situation where a Proxmox system’s KVM virtual machine refused to delete after the storage volume that it’s virtual HDD resided on was lost; trying to delete the KVM from the web GUI resulted in the following error:  
TASK ERROR: storage ‘proxmoxHDD’ does not exists
  Attempting to delete it from the command line using:  
qm destroy [VM ID]
  …resulted in:  
storage ‘proxmoxHDD’ does not exists
  Fortunately, there’s a way around this. The KVM config files live in:  
  Move or erase the [VM ID].conf file and when you refresh your web GUI the VM should be gone.

How to kill a KVM virtual machine in Promox via the command line or terminal

  Sometimes a Proxmox KVM VM will stop responding to the GUI’s attempts to shut it down; fortunately it’s easy to shut it down from the command line. Make note of the VM ID (next to the name of the VM in the left pane of the Proxmox GUI), log into the server via SSH as root and run:  
qm stop [vmid]
qm stop 124
  Check back in the GUI a few seconds later and you should see that the KVM has stopped.