You should alway have a good file based backup of any system.
If the dmgr installation becomes corrupted and you don't have a backup, you will need to reinstall the dgmr.
Even the "node recovery" option for node agents requires a new installation of the node agent.
You can backup the cell configuration, which you should also do regularly, and "import" it into the "restored" dmgr.
With WVE or Intelligent Managment you can configure a primary and a backup dmgr, and have them point to the cell configuration repository on a shared redundant storage device. You will need to use the ODR in this scenario.