A key in Nanodash stays with your account for as long as the instance exists. A command-line key is a file on your computer, and if that file is lost nobody can recover it. Nothing signed with a lost key can be superseded or retracted any more — those nanopublications stay as they are, and their content can only be replaced by new nanopublications made with a new key, which others will see as separate publications.

So keep a backup of a command-line key, and treat any key like a password: do not share it, and if it may have leaked, make a new one and stop using the old.