Ridley Scott's version of Alien's Xenomorph might just be immortal - let's examine the evidence. The impact of the original Alien on both the sci-fi and horror landscape can't be underestimated, and it's a testament to the movie's raw power that it still terrifies audiences over 40 years later. While the franchise would continue with James Cameron's Aliens, original helmer Ridley Scott was largely absent from the series in the years that followed, though he did mull a return for an early version of Alien 3.
Scott finally returned for 2012's Prometheus, which started life as a direct prequel before the concept morphed into more of a side story. The movie was highly anticipated, but despite being a huge success, it received mixed reviews that centered on its muddled screenplay and unlikeable characters. The same complaints were leveled at Scott's 2017 follow-up Alien: Covenant, which brought back the titular creature but played like an uneasy mix between the tone of Prometheus and a lukewarm Alien ripoff.
Alien: Covenant also presented a different origin for the title monsters than previous sequels, strongly suggesting that Michael Fassbender's rogue A.I. David engineered them as the "perfect" creatures. In general, it feels like Scott wants to put his own stamp on the series free of other iterations, and he took that a step further with Alien: Covenant. During a battle with one of the two Xenomorphs - dubbed Protomorph's - the main character Daniels (Katherine Waterston) crushes it in a crane arm, but Scott's own audio commentary reveals looks are deceiving.
He states that despite being crushed the Protomorph will start to reform once it's hit the ground, and isn't actually dead. Alien: Covenant itself doesn't even hint at this, but according to Scott the beast is "indestructible." This is likely the case with the other Protomorph in the movie, which is later ejected into space, but since the creatures have been shown to breathe just fine without oxygen, the suggestion might be it survived too.
It might be assumed that Alien: Covenant's Protomorph's are invincible due to David's genetic tampering, but if the creature from the original 1979's movie is evolved from David's experiments, that might mean it's also immortal. In the finale of Alien, Ripley blasts the monster out of the hatch of her escape shuttle before roasting it with the engines. The beast may have survived this, as it's shown in one piece as it flies off into the vacuum of space.
Having indestructible and immortal creatures would certainly prove David's point about creating the ultimate lifeform, even if it's not backed up by the other movies. James Cameron's Aliens showed that a concentrated blast from a Pulse Rifle fire will take care of a Xenomorph, which has also been shown in countless video games and comics. That said, this is Scott reclaiming ownership over the series, so to his mind, the beasts might take a grenade to the face just fine.
Scott's Alien: Covenant take is somewhat backed up by a more obscure source in Alien: Isolation - The Digital Series. This 2019 webseries attempted to adapt video game Isolation's cut scenes into a show with mixed results, but the finale reveals that the creatures don't die when blasted into space - they go into hibernation, waiting to be rediscovered. The idea the Xenomorphs are potentially unkillable might have played into the story of Scott's unmade third Alien prequel, but that's looking unlikely to happen now.