There's a couple of nice quotes from text 10 of the " History of Middle Earth " (Morgoth's Ring) that directly address the issue of orc immortality and orc lifespans: "
They needed food and drink, and rest, though many were by training as tough as Dwarves in enduring hardship.
They could be slain, and they were subject to disease; but apart from these ills they died and were not immortal , even according to the manner of the Quendi; indeed they appear to have been by nature short-lived compared with the span of Men of higher race, such as the Edain " Robert Foster's " Complete Guide to Middle Earth " notes that the average Edain lifespan is between 70-90 years, which suggests that average Orc longevity (barring illness and injury) is somewhere around 60 years of age .
It seems that the fact that certain (immortal) maiar were posing as Orcs gave rise to the myth that the orc race was immortal...
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.
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In his essay Myths Transformed , which can be found in The History Of Middle Earth vol.
10:
Morgoth's Ring , Tolkien explicitly states that the Orcs have a lesser lifespan than the Numenoreans.
This would suggest that they are long-lived, but not immortal.
The main evidence for Orcs being long-lived is the well documented dates of death of the Azog and Bolg.
Azog was succeeded by Bolg after his death in the war with the Dwarves some 150 years before the Battle of Five Armies.
Bolg then leads an army in that battle, so he is at least 150 (and presumably somewhat older).
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In The Two Towers , Shagrat and Gorbag were talking about the "good old days" before the Last Alliance: 'We'll see.
But anyway, if it does go well, there should be a lot more room.
What d'you say?
- if we get a chance, you and me'll slip off and set up somewhere on our own with a few trusty lads, somewhere where there's good loot nice and handy, and no big bosses.'
'Ah!' said Shagrat. '
Like old times.'
The Two Towers Book IV Chapter 10: "
The Choices of Master Samwise" So that would say they were over 3000 years old would it not?
Or am i wrong?
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We don't really know for certain, but it seems unlikely.
The narrative purpose of orcs is to be hordes of disposable arrow-fodder and the optimum design for such is "short-lived and fast reproducing".
I see no particular reason to think that Shagrat and Gorbash were talking about a time 3,000 years past, rather than just the situation that applied before Sauron once again gathered the orcs to his banner.
Tolkien did in fact go back and forth about the origins of orcs, but even if they did start as corrupted elves there's no particular reason to think they retained their divinely granted longevity.
If they had retained the eivish traits of great longevity combined with low reproductive ability...then the amount of warfare they engaged in, and how good they were at it would surely have led to their extinction.
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I don't know much about the orcs' life span.
But if indeed they were elves once, then they should be immortal because the gift of immortality and death was given by Eru.
Besides him, no one can change that, not even Manwë.
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In his essay "The Unnatural History of Tolkien's Orcs", the author "Tyellas" references the same passage from "Morgoth's Ring" (without quoting it or giving an accurate bibliographic reference)
that states Orks are not immortal.
He also makes good arguments, with similar references, for their "creation" as corrupted Elves.
As stated in this conversation, I am also of the mind that while Morgoth could corrupt Elves, he could not deprive them of their nature imbued by Eru.
Elves are immortal and can choose to return to Arda.
After they "die", they go to the Halls of Mandos to wait to return or until the end of the world, because they are tied directly to the fate of the world.
In corrupting them, I think Morgoth tried to deny them the choice of how or when to return, and he may have denied them the ability to coexist in the spiritual and physical worlds.
Besides corrupting them to evil, he could have bound them to an endless existence of a harsh life, a harsh death, and the inevitability of doing it all over again.
Kind of like the Tom Cruise movie "Edge of Tomorrow" or Michael Morcock's concept of the Eternal Warrior.
In the aforementioned essay, the author also makes a case for the potential of Orks choosing to become uncorrupted, which is in keeping with the idea that Elves can choose how they evolve throughout their immortal existence.
Reducing them to base instincts ensures there is always some Ork somewhere looking for an opportunity to breed, which in turn provides an opportunity for a fallen Ork to return - no extinction!
Daniel "Vaco" Vacaflores' article "Quendi" in issue 12 of "Other Minds" magazine (othermindsmagazine.com) expounds on the nature of the various types of Elves based on analyses of professor Tolkien's works.
In the article he discusses the consequences of their immortality and their ability to choose how they personally evolve through the ages, which provides the basis for the idea that Orks could potentially, though perhaps highly improbably, choose to become uncorrupted.
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Orcs were the most commonplace villains serving the Dark Powers in all of Tolkien's Legendarium, a race of sentient beings bred by the evil Vala Melkor (Morgoth) during the time of the Great Darkness.  If Orcs were made by Melkor (by breeding Elves he had captured and corrupted) then are they immortal?
Are Tolkien's orcs immortal?
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Orcs are long-lived, but not immortal.  The main evidence for Orcs being long-lived is the well documented dates of death of the Azog and Bolg. Tolkien states that the Orcs have a lesser lifespan than the Numenoreans; they are long-lived but not immortal.
Tolkien states that the Orcs have a lesser lifespan than the Numenoreans. The suggestion is that the Orcs are long-lived but not immortal.