WordNet (r) 3.0 (2006):

nonviable
    adj 1: not capable of living or developing successfully

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "nonviable":
   bad, despaired of, done for, dying, expiring, facing death,
   given up, going, hopeless, in articulo mortis, in extremis,
   incapable of life, low, moribund, near death, sinking, slipping,
   slipping away, terminal