The Jargon File (version 4.4.7, 29 Dec 2003):

netdead
 n.

    [IRC] The state of someone who signs off IRC, perhaps during a netburp,
    and doesn't sign back on until later. In the interim, he is ?dead to the
    net?. Compare link-dead.


The Free On-line Dictionary of Computing (30 December 2018):

netdead

    The state of someone who signs off IRC,
   perhaps during a netburp, and doesn't sign back on until
   later.  In the interim, he is "dead to the net".

   [Jargon File]

   (2007-09-02)