Não há uma resposta clara, porque as origens dos Orcs são obscuras. Supondo que, correspondendo à explicação publicada da origem dos Orcs, eles vieram dos elfos, proponho duas possibilidades:
Eles podem ter origem em Elfos, mas Morgoth rapidamente os cruzou com Homens quando eles acordaram e começaram a adorá-lo. Todos os Orcs imortais foram mortos nas guerras da Primeira Era e apenas Orcs misturados com Homens sobrevivem. Esses meio-elfos técnicos podem ter vida longa, mas não imortalidade. Os Orcs imortais nunca voltam porque se Fëanor é muito mau para reencarnar antes do Fim, então o Orc médio definitivamente é. Dito isto, alguns dos espíritos malignos no comando de Sauron e Morgoth são, talvez, os espíritos de Orcs imortais (ou mortais) mortos.
Mas, como alternativa, eu diria que dos Elfos ou não, seus destinos podem ter sido alterados por Eru e Morgoth. Considere o que Finrod e Andreth alegaram sobre os homens:
'Yet among my people, from Wise unto Wise out of the darkness, comes the voice saying that Men are not now as they were, nor as their true nature was in their beginning. And clearer still is this said by the Wise of the People of Marach, who have preserved in memory a name for Him that ye call Eru, though in my folk He was almost forgotten. So I learn from Adanel. They say plainly that Men are not by nature short-lived, but have become so through the malice of the Lord of the Darkness whom they do not name.
'That I can well believe,' said Finrod: 'that your bodies suffer in some measure the malice of Melkor. For you live in Arda Marred, as do we, and all the matter of Arda was tainted by him, before ye or we came forth and drew our hroar and their sustenance therefrom: all save only maybe Aman before he came there.1 For know, it is not otherwise with the Quendi2 themselves: their health and stature is diminished. Already those of us who dwell in Middle-earth, and even we who have returned to it, find that the change3 of their bodies is swifter than in the beginning. And that, I judge, must forebode that they will prove less strong to last than they were designed to be, though this may not be clearly revealed for many long years.
'And likewise with the hroar of Men, they are weaker than they should be. Thus it comes to pass that here in the West, to which of old his power scarcely extended, they have more health, as you say.'
(HoME X)
Assim, até o outono, os homens viviam mais e com maior saúde. A "malícia de Melkor" afeta até mesmo os corpos élficos, que não duram tanto quanto deveriam - milhares de anos em vez de até o fim.
Andreth até acreditava que os homens não deveriam "morrer" de todo, mas sim ascender ao céu corpo . Portanto, eu proporia isso: a "malícia de Melkor" naturalmente aflige os Orcs mais severamente. Mesmo se eles fossem imortais (por sua natureza potencialmente Elfica), seus corpos simplesmente desmoronariam. Então eles parecem mortais para nós, e não temos como determinar se seus espíritos permanecem na Terra-média (como os Elfos) ou se vão além do mundo (como os homens).Deve-se acrescentar, no entanto, que alguns Orcs eram imortais:
This last point was not well understood in the Elder Days. For Morgoth had many servants, the oldest and most potent of whom were immortal, belonging indeed in their beginning to the Maiar; and these evil spirits like their Master could take on visible forms. Those whose business it was to direct the Orcs often took Orkish shapes, though they were greater and more terrible. Thus it was that the histories speak of Great Orcs or Orc-captains who were not slain, and who reappeared in battle through years far longer than the span of the lives of Men.