It is possible to restore a removed unit if needed, or for example temporarily for renaming on old unit to reuse its name (see. Reuse unit name or unit code).
Go to Employees > Units. Tick the "show deleted" box in search options, and either search for all units or specify the unit's name in the search. You will receive a list of units, out of which the deleted units will have a "restore" button on their left hand side.
Click on this "restore" button, and the unit's is active again and it's information can be edited.