Alien totally abandoned Parker and Lambert...WHY?

[SM]

It's kinda hard to assume the xeno even killed Parker and Lambert.  Nobody knows if the head injury on Parker killed him, the guy coulda still had a heartbeat.  It's not even clear what happens to Lambert so we can't even say it was something lethal with certainty.

When Ripley stumbles on them we only see Ripley's face, not anyone else's.  Maybe she saw that they were unconscious [i.e. NOT dead] but also knew (sadly) that there was nothing she could do to help them without risking her safety too. She then decides to turn on her friends and get to the Narcissus and thus adding an extra element of tragedy to the overall story.  Her character arch however, makes a complete turn-around when she goes back to save Newt in Aliens. I think that James Cameron would agree because why else would he do this??

You did see Ripley's shudder of revulsion upon discovering the mess left behind by the Alien?

Still doesn't prove that they were dead.  I've looked at lots of living humans and shuddered in revulsion.  None of them were dead.

Even if both victims were still (barely) alive when Ripley arrived, how long do you think they may have lingered on before eventually succumbing.

As has been already noted; if there was a chance both victims were still alive, wouldn't Ripley have tried to offer assistance?

She saw the full extent of the carnage and realised both victims were beyond help - being VERY dead.

To answer your initial question, the answer is no.  It was in a time of crisis and she only had time to consider herself.  Jones is only saved as an afterthought and because he's light enough to carry.  Her reaction alone does not prove they died until she blew up the Nostromo.

She had all the time she wanted.  She could've easily checked if they were dead if she was unsure.  She was not unsure.

[Elmazalman]

To answer your initial question, the answer is no.  It was in a time of crisis and she only had time to consider herself.  Jones is only saved as an afterthought and because he's light enough to carry.  Her reaction alone does not prove they died until she blew up the Nostromo.

Spoiler

[close]

Parker was tough ... but not tough enough to survive this level of damage - same with his buddy, Brett.

[SiL]

But now I'm picturing Lambert just hanging by a mad wedgie, still quite a live, and Ripley deciding to nope out of there at the sight of it.

[Elmazalman]

But now I'm picturing Lambert just hanging by a mad wedgie, still quite a live, and Ripley deciding to nope out of there at the sight of it.

Can you picture where the blood is coming from...

[SiL]

A mad wedgie.

[SM]

That would be an acceptable reason to leave her behind and no court would ever convict her for doing so.

[Valaquen]

Theory: It was aware the Nostromo wasn't a safe place anymore, and retreated to the Narcissus.

That would be wildly precognitive of it.

The real reason is that the filmmakers wanted us to see the bodies. But it's fun to read everyone's in-universe speculations 

[Local Trouble]

Theory: It was aware the Nostromo wasn't a safe place anymore, and retreated to the Narcissus.

That would be wildly precognitive of it.

Unless it knew that Ripley was going to use it as an escape craft, the Narcissus wasn't exactly safe either.  Can the aliens glean knowledge from their victims like the brain bug from Starship Troopers?

[Elmazalman]

Theory: It was aware the Nostromo wasn't a safe place anymore, and retreated to the Narcissus.

That would be wildly precognitive of it.

Unless it knew that Ripley was going to use it as an escape craft, the Narcissus wasn't exactly safe either.  Can the aliens glean knowledge from their victims like the brain bug from Starship Troopers?

If the Alien was truly intelligent and had the ability to glean or absorb knowledge from its victims, it would have known about the self-destruct system, anticipating any human survivors plan to destroy the ship - it could have saved its nest onboard, and - most importantly - paved the safe 10 months journey to Earth for its eggs.

[razeak]

Yeah, Parker's brains got scrambled. There is zero intent or depiction that indicates Lambert is alive.

[The Old One]

I think I didn't articulate my meaning correctly, I meant that- gathering it's intelligent enough to understand the relationship between electricity and light, that suggests it's retreat to the Narcissus- somewhere comparatively quiet and dark, not loud and blaring as on the Nostromo suggests an instinctive intelligence that it understood the "main area" is no longer safe.

[SiL]

The blaring and light came long after it abandoned Parker and Lambert.

... well, minutes later, but still. Ripley didn't start the scuttle procedure until after.

[SM]

There was blaring horns and flashing lights in the shuttle too.

[Huggs]

It's one of those things doesn't make a lot of sense, but it was necessary.

They needed that last jumpscare for the end of the movie.

So in he went.

[SiL]

The shuttle was quieter than the rest of the ship. The sirens noticeably dip in volume when Ripley enters the Narcissus.