Spoiler alert! That's some pretty serious foreshadowing right there, and let's not forget that the hypersleep tubes look suspiciously like coffins. It's all just the subtle ways the film is letting your brain know that it'll be encountering death here.
DALLAS: Anything else?
ASH: Yes. There's rock—lava base. Deep cold, well below the line.
Everything about the planetoid seems tuned to be lethal to humans: the atmosphere, the air, the temperature, the ground, you name it. Without a spacesuit, it's insta-death.
DALLAS: He could die in 24 hours. Open the hatch.
RIPLEY: Listen to me. If we break quarantine, we could all die.
LAMBERT: Would you open the goddamn hatch? We have to get him inside!
RIPLEY: No. I can't do that, and if you were in my position, you'd do the same.
It's the old Spock conundrum; do the needs of the many outweigh the needs of the few? Ripley seems to think yes while Dallas is going with a no. We know Ripley is right, but we have the advantage of having seen how the movie comes out.
ASH: Now, we're assuming it's feeding him oxygen. If we remove it, it could kill him.
DALLAS: I'm willing to take that chance. Let's cut it off now.
ASH: You'll take responsibility.
DALLAS: Yes, I'll take responsibility. Get him out of there.
For the alien species, mortality isn't just something to take from the characters. It is a tool to use against them. It keeps Kane alive as if it knows that Kane's survival is necessary until it can accomplish its deadly task.
DALLAS: Anybody want to say anything?
And … silence. In Alien, there is no need to pray to a God for Kane's soul. Death is final.
LAMBERT: Could he want Brett alive?
LAMBERT: Could Brett be alive?
RIPLEY: No. I mean, I don't think so.
Fair question. As we learned previously, this species uses mortality as a tool allowing it to manipulate its prey. Only God—and some deleted scenes found only on your DVD—know what ultimately became of Brett.
RIPLEY: Unless somebody has got a better idea, we'll proceed with Dallas' plan.
LAMBERT: What? And end up like the others? Oh, no, you're out of your mind!
In movieland, Lambert's fear makes her about the last character we want to root for, since no one likes a crybaby. But in reality, let's face it, Lambert's reaction to mortality is one many of us share.
RIPLEY: Final report of the commercial starship Nostromo third officer reporting. The other members of the crew, Kane, Lambert, Parker, Brett, Ash, and Captain Dallas, are dead.
The final report contains the body count, complete with names. It is a chilling way to end. Instead of a scene of mayhem or a safe return, we get an enumeration of all the death that has come before.