system
Given the following post, respond as if you're commenting on Reddit:
human
[Man of Steel] How would have things changed for Clark if he had saved his dad?

Would the witnesses reported him?
If so, would the reports be believed by the government?
If so, what would Clarks life be like after? Would he be better prepared for Zod if the government had known about him earlier? Would he be autopsied by the government or could they come to an understanding?
gpt
Clark can't fly yet.  He doesn't have super speed.  Nothing in the movie indicates he can move people like playthings without hurting them.  Their cars are trashed and the highway is backed up for miles and there's no safe or fast way to evacuate Jonathan, Martha, and Hank (the dog).  They're stuck with the witnesses for the foreseeable future.  Certainly long enough to put together a convincing and reliable profile.

Unlike the kids on the bus who grew up with Clark and were saved directly by him, these witnesses owe Clark and his family nothing.  The world contains bigots and the fearful.  Clark gets reported- if not directly hounded- immediately.  By 1997 there was cellular technology.

This triggers an alert with Amanda Waller's pilot ARGUS agency so by the time the Kents get back home, the farmstead is already swarming in Men In Black.  They try to make a run for it, but Waller's task force are able to take the Kents hostage and compel Clark's obedience.  This hypothetical version of Clark didn't have the fortitude to obey Jonathan for the sake of the world, so he doesn't fight or run even when the Kents tell him to when their safety is at stake.

The catch of a Kryptonian, a Star Ship, and Command Key skyrocket Waller's importance, funding, and power accelerating the curve on metahuman study, capture, and exploitation.  A version of the Suicide Squad is assembled faster, with more advanced technology, and with Clark as an unstoppable closer.  Clark, meanwhile, is turning darker, embittered, and lost.  He can't answer any of their questions, he's routinely subjected to experimentation, and he's routinely reminded that Waller has her finger on the button to the bombs inside Jonathan and Martha's heads.  At some point, Clark is pushed to discover he can fly and suddenly he's not just a strongman but a god-like personal weapon of mass destruction who can act without a trace.  He's still not ready or able to kill for Waller, but he's coming closer and disappearing people for her making her assent to power easy.

Waller's more advanced power-curve means she's hunting the same prey as the Batman and they butt heads.  So Waller takes on the Batman.  It's a brief and hard fought war, but she calls in her ace and Clark ends Batman's career over his knee.  Waller imprisons Bruce and takes over his holdings with Clayface or a similarly powered metahuman.  Batman's research leads to additional metahumans and Waller has a stranglehold monopoly over metahumans on Earth... she crushes magic and removes the Amazons and Atlanteans as factors (not to say they're wiped out, but held in check) with her many pawns.

16 years later, the Scout Ship begins to give off a signal and it is discovered.  Clark is not told about it.  They plan to extract everything they can from it, but in the process, set off the beacon which summons Zod.

Zod sits on the darkside of the moon observing and researching the planet which is the only suitable candidate for terraforming they've encountered in 33 years.  In this timeline, Clark never went on the ship, never met Lois, and Lois never published her story about the Scout Ship.  While the tornado incident was reported, Waller's agency suppressed all records of that story shortly after, so Zod has no indication that Kal-El is on Earth.  He doesn't believe the Codex is on Earth, he has no reason to offer it an ultimatum, so after evaluating Earth's fighting capability to be harmless, he descends to terraform the Earth without warning.

With no advanced warning or plan, the World Engine gets much farther before Waller can even respond.  Metropolis is well and truly a crater by the time she sends her heavy hitters against the invaders' command ship.  None of them on are the scale of a Superman and get wrecked by the gravity weapon's effects.

Remember, they don't have Jor-El to give them a plan or explain what's happening.  Moreover they wouldn't have cracked his AI before Zod arrived.  They're essentially as ignorant as anyone else, except they recognize the technology as resembling Clark's.  Note further, they need the Jor-El AI's cooperation in activating the Phantom Drive on Clark's vessel to use it as a weapon (unless, in the real timeline, you think Clark never tried putting the key in after 33 years; doubtful).  So they wouldn't have that tactic available.

Waller's reluctant to show off Clark to the world, but there's no choice.  Gotham has been swallowed up by now, she orders Clark to take out the ship.

He rips through it, tears it apart, and shuts down the Black Zero.  HOWEVER, the World Engine pre-dates the Phantom Drive technology by 20,000 years and operates INDEPENDENTLY of the Black Zero (the Phantom Drive just makes it faster / more powerful).  The Earth is still getting terraformed, albeit more slowly.  However, out of the wreckage of the Black Zero comes Zod and his crew, powered under a yellow sun.

They're barely a match for Clark, who has been using his powers brutally for years now, but their numbers are enough to push him to kill for the first time, simply to survive them.  In the process, it dawns on Zod that this is Kal-El, that the Codex is on this planet, and this is the last son of Krypton, the son of his mentor, the son he was responsible for after killing Jor-El.

Held down by half-a-dozen Kryptonians, foaming at the mouth, Zod reveals this to Clark.

"YOU ARE NOT ALONE.  See our strength?  WE are your people."

Clark collapses and takes it in.  After his treatment at humanity's hand, 16 years removed from the kindness of the Kents and his hands stained with the evil Waller has had him do... he arises Kal-El, loyal to Zod.

While the World Engine works away, Zod and his dozens of powered Kryptonians start to assemble the Scout Ship, take out Waller's strongholds, and as a favor to Kal-El, rescue the Kents (a crippled Bruce Wayne manages to escape in the process).  The Kents try to appeal to Clark, but they've been so far removed from him, they're more like sentimental pets than a strong influence.  Clark wants them safe but he can't relate to them anymore.

Waller was powerful, but she didn't end everyone.  The remaining world powers and significant metahumans take out the World Engine and stop the terraforming.  Zod is enraged, retaliates immediately and the last of humanity's resistance is destroyed.  From the Kal-El's vessel, the Phantom Drive is recovered and retrofitted to the Scout Ship, with intentions of fetching a new World Engine.  Zod entrusts this mission to Faora, to bring back a World Engine so that Krypton can begin a new.

However, the remaining Kryptonians aren't so ready to return to a life of servitude under Zod, now that they've enjoyed Superman-level power and used it to crush Waller, etc.  As soon as Zod's second in command is gone, Jax-Ur plots to kill the Kents, frame Zod, to turn Kal-El against him.  Once they've battled and weakened, Jax-Ur and his coup kill Zod and Kal-El and claim Earth.  Kryptonians become the dominant race on the planet, then spread throughout the galaxy like a plague.

----

Jonathan was right.