In the old script of Alien: Covenant (2015), the Xenomorphs that Daniels defeats on the flying platform, is shown to regenerate his wounds once fallen back on the planet surface. In the Alien: Covenant commentary, Ridley Scott repeats this concept and explains that on the planet, the wounded Xenomorph regenerates itself. When I first heard Scott’s words I thought that the director was simply implying that, being the DNA of the old pathogen extremely powerful and indestructible, the body of the dead Xenomorph would have turned in something else, simply because its DNA was made to incessantly transom life. But maybe Scott was really implying the Xenomorph is “immortal”, since in the old script is clearly explained that the alien was meant to heal the wounds on its head (Daniels shot it in the head from a very close distance, in the old script) once fallen in the dead city.
It has been long established in the books that the Xeno can heal and the facehugger too. It was part of Dan O'Bannon’s original idea to make the alien a formidable enemy that’s not easily killed.
Alien 1979 Novelisation
Chapter VI
• Ash was examining the section cut by the laser knife. ‘Healed over. No sign of the wound. Remarkable regenerative abilities. You’d never know it had been touched.’
Chapter VII
• ‘What about the creature? We know now it can leak acid and heal itself fast. Anything else we know?’
Chapter XI
• From your description of the creature it’s now extremely fast as well as large and powerful. I think it’s reasonable to assume it retains the same capacity for rapid regeneration as its first “hand” form. That means you’d have to kill it instantly or it would be all over you. ‘Not only would that be difficult to do if your opponent were a mere man, it’s also virtually impossible to do with this alien because we have no idea where its vital point is. We don’t even know that it has a vital point. Don’t you see?’
• All six wounds heal fast enough to preserve the alien’s life, but not before it’s bled enough acid to eat numerous holes in the ship. Maybe some of the stuff burns through the circuitry monitoring our air supply, or cuts the power to the ship’s lights. ‘I don’t consider that an unreasonable scenario, given what we know about the creature.
Chapter XII
• ‘Why not,’ commented Ash, ‘with its inbuilt talent for regeneration?’ The engineer continued, sounding every bit as disappointed as he felt. ‘We had the bastard. We had him.’ He paused, added, ‘When it pulled free of its limb, it bled all over the place. The limb did. I guess the stump healed over fast, lucky for us. The acid ate right through the hatch. That’s what caused the depressurization.’ He pointed shakily towards the door sealing off the airlock vestibule from the rest of the corridor.
