Headscratchers / Terminator: Dark Fate

Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.

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Why did post-T 2 Sarah Connor imagine that a post-nuclear nation in Central America would erect WWII-style anti-tank obstacles on their beaches?

The movie even shows in-universe why not to bother with that. Sarah would know that’s not how it would play out, given her obvious connections to arms dealers specializing in US military-style weapons.

• Sarah hasn't seen plasma weapons or hunter-killers either. It's a day-dream, dreams don't have to make sense.
• They may be there to force Skynet to use Terminators instead of tank HKs. We also see Terminators get killed with just one or two plasma shots. The tanks are presumably a bit more durable than that, hence why the resistance might want to bother with the anti-tank stuff.

How was sending a cyborg, with pretty intense medical needs, a better idea than sending a re-programmed terminator?

That probably has something to do with Legion's Terminators being much more deadly in proximity, given how they have a liquid exterior that can and will kill you without any easy means of incapacitating it. So far, only endoskeleton Terminators have been reprogrammed in any alternative media (and T2), with the possible(?) exception of Catherine Weaver in Terminator: The Sarah Connor Chronicles. Since Legion doesn't seem to be making any of those, sending Grace back would've been their best option in spite of her weakness.

• Also, its a different future and a different Resistance. This Resistance simply might not have the capability to reprogram Terminators. Or maybe Legion's Terminators are impervious to reprogramming, possibly for the reasons mentioned above.
  • This, Skynet was an AI from the 90s, early 00s and is a very simple AI that attacked humanity based on the assumption that humanity was a danger to the AI and an old AI learning to self-improve is incredibly unlikely despite modifications, like learning that under all those Add-On your Windows 10 is just a pretty MS-DOS. Legion is an AI from the new 20s, its motives are unknown and it is implied its first tactic was to wait for humanity to kill itself out of desperation before deploying Terminators that by the way, even try to negotiate and emulate charisma pretty quickly. Also, its name implies some kind of hive mind making reprogramming very hard.
  • Additionally LEGION was originally designed for cyber-warfare; its main purpose is to prevent exactly this scenario, so it would be very difficult if not impossible to reprogram these terminators assuming you even had the equipment to do it.

Why does Sarah Connor say "They never learn." when she hears of Legion's existence? All the evidence and witnesses from the 2nd movie are gone by the start of this one. There wasn't ever a lesson given.

• One could infer that she means that humanity never learns, in that trying to build an artificial intelligence will just result in the destruction of humanity. And to be fair, she's not wrong considering all the evidence supporting it not once, but twice.
  • To say nothing of all the tropes about it.
  • Which is, ultimately, why Judgement Day is inevitable. Humanity isn't going to figure out that making military A.I.s is a bad idea on their own, it has to catastrophically blow up in their faces first. Judgement Day and the war against the Machines is unfortunate but has to happen so the world can realize not to do this crap again. The time travel constantly prevents this lesson from being learned and allowing humanity to rebuild because the timeline keeps getting altered all the time.

Somehow, Legion figured out how to make "Send assassins into the past and kill that one irritating human" a viable strategy, but not "Deploy a global network of geosynchronous spy satellites and watch every inch of the earth, 24/7."?

• The Rev-9 on its own is shown to hack into surveillance cameras and drones and scan for its target pretty quickly. Who's to say Legion hasn't already done much more in the future?
• That could be what those mysterious monolithic towers are for, Global Network Towers.

Sarah Connor somehow solo'd some unspecified number of terminators between the 2nd movie and this one, when there's not a single cinematic terminator she could take on without help? Is Legion spectacularly inept compared to Skynet?

• The key difference between the mentioned encounters in Dark Fate versus with the Terminators in 1 and 2 is that Sarah isn't prepared in advance. Granted, in T2 she's got friends who can provide her weaponry to gear up against an apocalyptic future, but that doesn't downplay the fact that she started off under-equipped for the job. The fact that Carl has been sending her texts of the location and time when a new Terminator comes back, gave her ample time to gear up and prepare.
  • Also, it’s heavily implied she simply camped a location for a spawn-kill each time. The one good thing that came from Genysis is to show a Terminator is fairly easy pickings with prep time and forewarnings.
• Legion is also twenty-some years more advanced than SkyNet, with twenty-some years more advanced technology to work with once it decides to Kill All Humans. SkyNet's weapons platforms are extremely formidable, but once you have the tools to take them down, they die just fine. What makes T-800, 1000, and X series Terminators so formidable in the modern day is that you need weapons of destructive potential not readily available (armor-piercing anti-tank rounds or rockets for a T-800, temperatures equivalent to molten steel for a 1000, and gods-only-know-what for a T-X). If you know a T-series Terminator is coming, and you have access to tools to destroy it, it's not that much of a challenge compared to facing one with whatever you can scrounge in between fleeing for your life. Comparatively, Legion's REV-series Terminators are so advanced they require future technology to have a chance at putting them down, and even that isn't a sure thing. Reflecting how rapidly technology has advanced between the 1980s and 2010s.
  • And this is basically Sarah's fault. Every time she succeeds in postponing Judgement Day, when AI does eventually evolve the technology of the era is just that much more advanced.
• It is implied that the Terminators that Sarah had been facing through the years were all T-800s sent by Skynet, and the Rev-9 in the movie is the first of its kind that she has seen.

Was Dani Ramos always the target of the terminators between T 2 and Dark Fate?

• If by "New John Connor" you mean Dani Ramos, then no, Those Terminators were sent by Skynet from the original timeline to kill John Connor. Of course, they arrived in a world where John Connor had already been terminated and the rise of Skynet had been prevented.

How did Sarah fight ALL those terminators without becoming privy to better information?

It's implied somehow 40 years of fighting passed without her accomplishing much more than simply killing the terminators that showed up. She never even bothers to figure out who takes Cyberdyne’s place.

• How is she going to get that information? No previous Terminator has ever been forthcoming with information. The only reason the audience learns anything is because of the forces sent back to help, and they are just giving a history lesson. Their missions were to kill her and prevent John Connor from becoming leader of the resistance. None of them are going to have a chat first.
• Interesting observation, however: were those terminators Skynet’s or Legion’s? Maybe one of the terminators Sarah killed was supposed to kill Dani’s mother or something...
  • They were from Skynet. Carl is from Skynet, the implication being that Skynet was still destroyed in the future/never created in the past, but still was able to send back multiple Terminators to kill John. Those models were still programmed to hunt and kill him, they just came from a timeline that no longer existed due to John and Sarah's actions.
  • The Terminators that Sarah intercepted were definitely sent by Skynet to kill John. People seem to be confused by the fact that they arrived after John's death so it seems to make no sense that they were sent to kill him, but remember, time travel... Presumably, Skynet deployed them all at the same time but to different temporal destinations to hedge its bets.
  • To be fair, it shouldn't make sense since the tipping point between Skynet and no Skynet is Cyberdyne's destruction in T2. From the perspective of Skynet, their terminators should be landing in a timeline where they weren't wiped out, instead of breaching into one where the course of history was changed to prevent their existence. The only time locations they could possibly get to in order to make it through the altered timeline is before the events of T2, since both timelines would share that same history.
  • If the Terminators Sarah hunted throughout those 2 decades were Skynet ones, it's weird why Carl decided to rat them out. With John Connor dead, they'd presumably all turn peaceful like he did (which doesn't make sense, but that's a Headscratcher on its own), being that they're computers, and should work in a deterministic fashion. If they were Legion Terminators, it stretches the believability that Sarah would be able to hunt them down, as all of the Legion Terminators we see are way more advanced than the T-800. Hell, if any of those Terminators was a T-1000, Sarah would be in huge trouble on her own.
  • To Carl, they are just disposable machines. He is trying to make reparations for what he did to Sarah, so he is giving her some catharsis and something to live for. She can't kill the T-800 that killed John, but she can kill others. And all of those others run the risk of creating a new Skynet. He also has no guarantee that they will turn out as benevolent as him.
  • Those Terminators definitely were not Legion's, Sarah made clear to Grace that she had no idea what a Rev-9 was. Also, logically it would make 0 sense for a Legion to send Terminators against Sarah, since in Legion's timeline she was not important.

After failing 20 or so times (one terminator every two years), Legion never comes up with a different goal for its assassins?

• While it's not explicitly stated, the other two Terminators Sarah alludes to killing were almost certainly sent by Skynet from the original future. Sarah mentions how Skynet sent multiple Terminators back to kill John, including Carl. The two other Terminators it sent were likely among those.

After sending T- 800 and T- 1000 back in time to kill John Connor, both failing their mission, why does Skynet suddenly go back to the inferior model for the 1998 mission again?

• The T-1000 was a prototype. It was likely the only one that it had to send. The implication in Dark Fate seems to be that Skynet sent a T-800 after Sarah in 1984, a T-1000 after John in 1994, and a few more T-800s in the years after. Because of the nature of time travel, we have no way of knowing when any of these Terminators was deployed relative to each other. All of the T-800s could have been deployed before the T-1000 was even complete.
• There's some source material that states that the T-1000 are too good at learning, and Skynet doesn't want a rival. They're likely too difficult to manufacture en masse as well, at least by the time Skynet needs to send the first one back in time to kill John Connor.
• Also, it's entirely possible that the T-800 that would become "Carl" was sent back earlier than the Terminators from the previous films. Skynet probably deployed a bunch of T-800's to different points in time, including Carl being sent to 1998. When the Resistance smashed the defense grid, it activated its desperate last-ditch plan of sending a T-800 to 1984 and sending the T-1000 to 1995. The T-1000 was most likely, from a sequential perspective, the last to be sent back, since the events in 1995 caused by its arrival are what leads to Skynet being erased from existence.

Why does Carl get a life and a family after eliminating its primary target?

In T2 we learn that the terminators sent out alone, that most likely includes Carl as well, have their chips set to read-only, and only after John sets it to read-write in a deleted scene, the Terminator starts learning and behaving like a human. There was nobody around to perform the same surgery on Carl.

• That's only true for the extended cut of the movie, and thus its canonicity is debatable going forwards to Dark Fate.
  • The extended cut only shows the procedure itself, while the conversation where T-800 explains the nature of its CPU and its learning abilities while Sarah is extracting the bullets from its back is present in all editions of the movie.
  • I fished out a DVD copy of the theatrical version to check, and this is word for word what John and the T-800 say towards the end of the scene:
  John: Can you learn stuff that you haven't been programmed with? So you can be... you know, more human, and not such a dork all the time?
  T-800: My CPU is a neural-net processor, a learning computer. The more contact I have with humans, the more I learn.
  John: Cool.
  • Whoops, sorry. Thought they kept the "Doesn't want you to do too much thinking, huh?" conversation in theatrical cuts. So that means that the manual RO/RW switch is non-canon now. Didn't make much sense anyway.
  • Good question. That occurred to this troper, and this troper has two possible explanations:
    • I assumed based on Carl's dialogue that he didn't just have secondary objectives for if he succeeded in killing John that were all rendered moot by the Skynet timeline's derailment; he literally had no missions except to kill John programmed into his CPU, because Skynet was in a rush to send Carl back in time before the Resistance fully destroyed Skynet or seized its Time Displacement facilities. If that's the case, perhaps Skynet didn't have time to set Carl's CPU to read-only and so Skynet reluctantly sent him through the Time Displacement Sphere as he was as quickly as possible.
    • Carl could've, once he was purposeless after completing his mission to kill John, maybe blackmailed or manipulated someone into setting his CPU to read-and-write so he could learn and seek new purpose.

All of her cybernetic implants, and they couldn't give Grace an internal insulin pump (a technology that already exists) and internal autoinjectors for all the other drugs she needs to function?

Means nothing if she doesn't have a ready supply of the drug. Still needs to be refilled.

Since when are Humvees that watertight?

• Technically, they’re not. But some variants are built and/or modified to resist gas attacks. If you can block a gas, you can certainly block a liquid, at least for a time.
• There is actually a military term for it, "buttoning up", usually that means sealing off a vehicle for gas or liquid attacks, judging by the fact that the hummers were in the plane, and ready for parachute deployment, they might have already been mostly sealed up to withstand air pressure changes, such as, say, being dumped out a plane.

• So security is just going to take this Border Patrol agent at his word when he says he has metal implants? No asking for a doctor's note, no "Show me the scars." or anything like that?
  • They also let a complete new face pass through just because he was wearing a uniform, with no documents required, so they were just bad at their job.
  • There's a similar problem at the Air Force base. They would never allow a vehicle to come in hot like that, even with an officer radioing ahead. Also, there would be vehicle countermeasures like concrete barricades in a serpentine layout that would prevent them from driving straight in. The flight line also has its own security checkpoint. They wouldn't be able to just take a C-130 like that. It has a specific mission, which is why equipment is being loaded or unloaded. It takes time to run through the pre-flight checklist and get everything going; something like fifteen to thirty minutes. I don't recall seeing anyone pull the wheel chocks from the landing gear either. And while we're on the subject, why are the Border Patrol agents so blase about Grace breaking free from her restraints and a drone landing on their position? I think some of the agents died in the explosion, and we just cut to boring business as usual.

Why is the turbine in this dam exposed?

What's to stop someone from stumbling and falling into it?

• Standards of health and safety imply that people who are around such items aren't stupid enough to go near them without good cause. I think I remember temporary safety barriers around it, maybe it was in the middle of getting fixed?

Grace's tattoo

Grace has a tattoo of coordinates, that point the group towards Carl, who has also been supplying Sarah with coordinates of enemy Terminators. Grace mentioned that her commander gave her that location in the future. So, is future-Dani aware of what has happened and is engineering a stable time-loop?

• Probably, that's pretty much par for the course when it comes to Terminator movies.
• Word of God confirms this in a recent interview.
• This makes future Dani cold as hell. She knows she's sending her subordinate, who absolutely worships her, to die, just to save her own ass. Kinda beats the "we make our own fate" thing they were going with for the climax, too.
  • It's a throwback to John Connor and Kyle Reese. And like Connor and Reese, Dani isn't sending Grace back solely to protect her, she's sending Grace back to protect humanity as a species.
  • John Connor has a slightly different set of circumstances. He never met his father, he didn't exactly die in his arms when he was younger, while he vows to change the future. And he's sending the guy to save his mother, so it's a slightly more selfless act, even if it also means saving his own behind. Dani went through all of the events of this movie, got to know Grace, and then 20 years later sent her as a sacrifice even though she went through all of that stuff T1 John never experienced when younger.
  • But Dani does vow in the end to take steps to prevent Grace from dying 'again'. Presumably, Future!Dani also decided to do so. In fact, it's possible that's how the loop involving the tattoo came about - in a previous timeline, Grace may have been sent back without the tattoo, events may have progressed slightly differently (with Sarah being the one to track down Carl instead), but Grace ultimately ends up sacrificing herself. Dani, in a bid to prevent Grace's death, gives her that tattoo hoping that getting Carl involved earlier would alter events enough. But unfortunately, Grace still ends up dying. Now the Dani we follow in the film might have to try something else...

While Carl and Grace are busy trying to push the Rev- 9 endoskeleton into the turbine, why doesn't the liquid metal part detach from it and kill Dani?

• Can't detach it when it's using it to make claws and resist being pushed in.
• It was also forming its "skin" into blades to repeatedly stab at Grace and Carl, like it did when it got dogpiled by the Border Patrol. It didn't help (especially against Carl), but it was trying everything to get away. The Rev-9 seemed to very quickly realize that turbine posed a substantial hazard to it, and it seems likely the liquid metal skin can't operate indefinitely from the endoskeleton. We only see them separate for brief periods, and the endoskeleton never leaves the liquid metal behind, even when that means suspending the chase for its primary target.
• I figure the Liquid part of the REV-9 is "slaved" to the REV-9 solid unit, the REV-9s "brain" controls both halves, being a computer, it would be like running two programs at once, the liquid being a "slave" unit meant that it is subject to override by the solid unit, at that moment, the solid unit was commanding the liquid unit to save the solid unit, as if it separated there is a good chance the solid unit would have been destroyed or too damaged to function by the turbine, the liquid unit took the brunt of the damage when it went in.

What was the relationship between Sarah and the USAF Major where despite being the most wanted woman in the US who almost immediately got singled out by the Feds after captured by the Border Patrol, he immediately gives her two EMP devices, hands her a transport plane to escape in and even assigns two F-35's as escorts?

• Blackmail? He's selling hardware on the side? Sarah had militia contacts, maybe they gave her some dirt on him. Sarah does say that Carl is a member of her "operations team." She might be posing as a black ops unit. She's getting military-grade hardware from somewhere after all, and he knows something is up if he's willing to give her an aircraft and an escort. He might even know about Terminators for all we know.
• It's pretty open. Maybe he was present when an earlier Terminator arrived and Sarah killed it. Maybe he's an adult Danny Dyson, and so understands Terminator history. Could be anything.

Why does the Rev- 9 wait until the group is captured by Border Patrol before he turns the drone into a projectile instead of any time sooner or then not even wait a few moments until they are in a car with no way to escape his attack?

Drone footage might not have been great and it wanted to make sure it was the group he was targeting, not just a random party of illegal immigrants. It waited till there was confirmation that Dani was there and took the first opportunity to attack her.

How did Dani and Sarah locate Grace's child self at the end?

Grace never gave her full name.

Why did "Carl" have a life-changing crisis after his objective was complete?

Wouldn't Skynet make sure their Terminators have protocols in place for what they should do after they're done with their mission? Keep in mind that they use the things on infiltration missions in the future as well, so having an "escape and come back to HQ for your next assignment" protocol should come with the territory. A Skynet Terminator that knows Skynet was destroyed should probably decide to try reverting that or, failing that, go into "hide and kill every human who figures out what I am" mode. This all goes double for a Terminator sent to the past, having them just doing whatever they want is just opening up possibilities of further changes to the past, completely out of their control (like, say, humans coming across this peaceful Terminator, and figuring out ways to counter its defenses).

• Sending the Terminators back in time was a desperation move; John Connor and the resistance were in the mop-up stages of the war. Part of making sudden moves in desperation is that you really don't have the time or inclination to think of every single contingency. In addition, let's say they do have an "escape and come back to HQ" failsafe. How on earth is Carl going to do that, in 1998?
  • That's part of my point, sending the Terminators back in time may have been a last-ditch effort, but the usage of Terminators was not. They were regularly issued in non-time travelling infiltration missions in the future, and that's exactly why they should have post-mission protocols. As for what Carl would do if he had such a protocol, it would be either physically going to the place where Skynet was going to use as its center of operations in the old future and going standby awaiting further orders, or just fall into an endless cycle of trying to reach a place that doesn't exist, it certainly wouldn't result in "learn self-determination". And that's assuming the Terminators are not true AI, if they are true AI, he would basically be Skynet himself, so he would probably just take Skynet's main goal as his own.
    • My theory (since the way Carl talks in the film about being purposeless after he completed his mission seems to hint his CPU was programmed with zero backup objectives rather than them all being rendered moot by Skynet's derailment) is that probably, Skynet was in a rush to get as many Terminators as possible sent back in time before the Resistance fully destroyed it or seized the Time Displacement facilities. So it made a calculated risk of sending Carl back with only the most important mission programmed into his CPU.
• You're forgetting a major element which very likely played a part in Carl's "life-changing crisis" - the fact that Skynet was effectively wiped from existence! Once Carl realized that Skynet's rise had been prevented and that its creator/master would never exist again, his programming probably broke down, allowing him to develop more independent thinking in search of a new purpose. Skynet likely never anticipated the possibility that its time-travel missions would somehow prevent its own existence and so didn't program the Terminators that eventuality.
• Skynet is nowhere near as imaginative as a human. Why not have a T-101 sent to 1975 and gradually locate Sarah? Follow her and learn every detail about her life and then leave the info in a bunker that Skynet knows survive the war so it has perfect intelligence to locate Sarah? Because it has only been able to come up with a simple series of ideas, ie "kill John Connor", "kill his mom before he's born", "kill his helpers". Doubtless the idea of secondary missions and failsafes never occured to it.

This film, like Genisys, seems to confirm the multiverse time travel theory

Carl continues to exist after Skynet's destruction This, along with Cyber-John's arguments in Genisys, strongly suggests that history can't be changed. You can go to another universe and change things there, but nothing's going to change for the people you leave behind regardless of what you do to Grandpa. Doesn't this break the central concept of the series? If you can't change your own past, time travel can't be weaponized.

• There is nothing to indicate that history isn't being changed. Time-travelers themselves may continue to exist as remnants of the original timeline, but the futures they come from have been erased from existence. And even if that isn't the case, and the original timeline still exists somewhere, it doesn't affect the story. Neither Skynet nor the Resistance really know how time-travel works or what its consequences truly are. Even if the reality is a branching-timelines scenario, both sides might assume that they can rewrite their own history with time-travel.
• Forget what was said in Genisys. In this movie's version of the story, the future can and has been changed. Skynet was destroyed in T2. Carl being sent to a past after T2 is either a plot hole, or he was actually sent to some time before T2, and just took a long time to find John. Once he was in the past, he "survived" the change in the timeline.
• For the latter explanation, try to think of the timeline like a Y-shaped river. \ is Skynet, / is Legion, | is their common history, i.e. before Cyberdyne was destroyed in T2. Both timelines exist, but can never interact with each other anymore. Skynet can also never send Terminators from \ to /, but they still have access to |, which could allow Terminators to go in either direction depending on what they do.
• Remember Avengers Endgame? It appears the Terminator franchise run on a similar system of time travel i.e. multiple parallel timelines going on at the same time. Travelling in time merely creates a new parallel timeline. The past of the timeline you came from can’t be altered. This is opposed to the Back to the Future model, where there is a single timeline that can be altered drastically trough time travel. Now granted, all the various Terminator movies give contradictory hints of working under one system or the other.
• It's unclear as to when Skynet sent Carl back or what year he was sent to. Given that he looks more or less the same "age" as Uncle Bob in 1998 he was probably sent directly to that year before Skynet sent back the T-800 and T-1000 in T1/T2, and was most likely the first one sent since Sarah and John came across no other Terminators since 1995. It seems that Skynet might have sent back a bunch of T-800s post-Judgment Day (1997) throughout a bunch of different years to attempt to kill John Connor before he could organize the resistance (which failed), and the events after sending back the T-1000 erased Skynet from existence but not the T-800s it had already sent back. In the original 1998 Carl would've failed and been destroyed, but the past being changed via Skynet's erasure is precisely why he was able to succeed.

Why doesn't Carl kill Sarah before/after murdering John?

She has to at least be a secondary target for termination.

• Not necessarily. Skynet tends to have tunnel vision with regards to John Connor, and probably doesn't even regard Sarah as a threat (unless it's in a time period before she gives birth to John). It's also possible that Carl was sent back earlier than the T-800 sent to 1984 i.e. before Skynet even thought of Sarah as a potential target.

How did Sarah work out that Carl was the Terminator that killed John, and not just another off the assembly line?

The Terminator that killed John was young-looking. Carl is old-looking.

• The very distinctive scar on his right cheekbone.
• She doesn’t know for sure, she sees the face of her son’s killer and reacts with emotion rather than considering the possibilities.
• She was getting texts of the other terminator's locations saying "For John" from his house, which let her know whoever lived there knew something about it. Carl being that terminator was the obvious conclusion. Besides, she's personally destroyed every other T-800 she knows of, it's not like there were any other options.

What is the Rev- 9 endoskeleton made of that it can be struck by an 72 LAW M 72 LAW rocket

, which uses a [[https://en.wikipedia.org/wiki/Shaped_charge shaped charge that can pierce a hole in up 12 inches of steel and disable or destroy tanks, and not even show so much as a scratch?]]

• Gabriel Luna has vaguely referred to the Rev-9 as being constructed of some sort of carbon-based alloy. No material currently exists that can replicate that sort of durability.
• Honestly, the only realistic explanation I can think of is that the extremely skeletal design of the Rev-9 allowed the shaped charge to break up and/or pass through the endoskeleton without hitting critical components, like how Grace pinned it with rebar.
• Everything travels along the path of least resistance. My theory is the Rev-9 endoskeleton was light enough that the force of the shaped charge going off was enough to send it flying, without providing enough resistance to penetrate its structure. Tanks and other fortified structures are extremely heavy and don't move around at any significant speed.
  • The weight of the Rev-9 endoskeleton shouldn't matter much. Getting knocked back will disperse some of the force, but the terminator would still need to be tough enough to survive the initial impact. A shaped charge works by projecting a thin jet of metal to ~Mach 30 (faster than the detonation velocity of most explosives) into the target - any realistic armor material would be penetrated. It would be a bit like getting hit with a APFSDS cannon round at point blank range. The Rev-9 would still have to be unbelievably durable for the above scenario to occur.
• Still the durability of terminators has always varied based on the source. The original T-800 in Salvation shrugged off a 40x46mm HEDP round which can penetrate 2 inches of armored steel. In comparison, in Genisys, a single .50 BMG sabot round (which should have less penetration than the 40x46mm HEDP) from close range disabled the T-800 first seen in Terminator 1. Then in Terminator 3, the T-X survived a hit from a RPG-7 but had several systems damaged beyond repair. So I guess we can just sum it up to writers not knowing weapons well?

How do Sarah and Dani clean up all the Terminator tech from the dam before the authorities arrive?

(Presumably, they could throw Grace in a truck or something.) They've conspicuously destroyed a major piece of infrastructure and Carl and the Rev-9's remains are fused to the bottom of the turbine.

• They might have just left them there. Given that they were fused to the floor in a place that would be difficult to reach, they likely didn't have enough time to dislodge and move over 400 pounds of metal before firefighters and police arrived, and given that they were almost completely melted, it's unlikely that either of their processors are salvageable, so it's unlikely that anything bad will come of leaving them there.
• They might have decided there's no point because they're not trying to prevent Judgement Day anymore. Consider these two things: Sarah, John and Uncle Bob derailing Skynet's creation only led to the rise of a new Crapshoot A.I. after humanity got an extra few decades, and it created a timeline where Sarah had to watch her son die and put him to rest whereas Reese told her that in the original timeline it was the other way round, so Sarah's probably reluctant based on that to dare try averting the Bad Future again; and Grace's flashback of Legion's uprising, where she's played by the same child actress as in the film's final scene, seems to indicate that Legion's uprising is only literally a few years away at most in the film's present day.

Putting aside that she kept removing it, would Sarah’s trick of hiding the phone in the foil crisp packet work?

• Having just tried it myself, I can say my phone can still receive calls even in a chip bag.
• It can work, but it depends on both the type of phone and type of packet used. In 2017 an Australian man was fired from his job after using that trick for several years to go play golf while on company time. He was discovered when someone reported seeing him on the fairways, and the company found that that it matched with the times when his "glitchy" phone lost signal.

Since anyone who looks like the T- 800 is wanted for being a Cop Killer, how did Carl open up a business and get a comfortable life in Texas?

• Given that the only photos of the T-800 are low-quality CCTV images, and Laredo and Los Angeles are over 1,000 miles apart, it's possible he could avoid being identified, which would only get easier as time went by.
• Also, Carl probably doesn't know the specific actions of the T-800 that was sent to 1984 other than the fact it failed, similar to how Uncle Bob didn't in T2 until John and Sarah told him. And even if he did, he kept a low enough profile for well over twenty years without being discovered.

How does Carl self-terminate?

At the end of T2, it is established that a Terminator can not "self-terminate", requiring Sarah to press the button to lower the T-800 into the crucible. How is it then, that at the climax of this film, Carl is able to willingly and knowingly destroy itself while taking Rev-9 with it?

• There's no voluntary self-termination going on the T-800's part; rather, he's being destroyed whilst pursuing the goal of destroying the Rev-9. Alternatively, you could look at it as a case of Grew Beyond Their Programming, given that Carl has had longer than Uncle Bob to stick around.
• There is a difference between 'this will kill me' and 'I will die if I do this, but it will accomplish my goal.' We have seen this distinction previously in the now-non-canon T3 wherein the T-X is killed by the T-850 jamming its ruptured final power core into 'her' mouth and blowing both of them up. Based off of this evidence, a basic bit of logical coding written into Terminators as a failsafe must be something along the lines of: "If the only result of this action is my own destruction, null action. If this action will accomplish my mission BUT also destroy me, take action."