What if, Celestia didn't know that the Elements simply banish her? What if, she saw Luna got consume by blast and thought she got vaporize or something like that? What will this change?

Posted this on other group a couple of days ago, not sure why I didn't also post it here.

7830950
A long slow tragedy of Celestia struggling with the pain of killing her sister probably. Maybe she develops some erratic tendencies as she tries to cope with the perceived loss.

7830950
In the actual show timeline, nothing would change, except for Luna's absence. Celestia would cope with it over the millennium, the powers of Harmony/destiny would find some other target for the baptism of fire for Mane 6, and all would be pretty usual.
In the global scope of things, the tragedy of Luna is that she can be viewed as pretty insignificant. I currently have a short story that alludes to it.

7830950

Try to put yourself in the place of Celestia, just imagine yourself in her role, at least for a few seconds. Then you will get an approximate answer to your question.

Personally, I would take off the crown and the duties of the ruler of this kingdom. After that, I would go to live in the forest as a hermit. Because this event will cause a strong mental shock. To sacrifice the only sister, for the sake of their little ponies, who for some reason did not pay due respect and attention to the Princess of the Night, would damage sanity.

The plot of the canon has a lot of illogicality, covering it all with magic. Personally, I am still trying to understand all this, including the principle of operation of the elements of harmony.

They turn someone into stone (a very humane way to defeat dark energy), and send someone to the moon... Even priests will be stronger than these elements of harmony when they cast out the demon from the human.

Celestia probably wouldn't send her student to make friends at Ponyville, thus rendering the Elements useless.

She would then have a moment of, "Yay my sister's alive," which would be closely followed by "Oh no, my sister's alive," due to the fact her sister randomly appears still full of hate after her banishment. There would then be a fight between the two which Nightmare Moon may be prepared for, while Celestia didn't see it coming.

7830998

In this reasoning, you are missing about a thousand years of Celestia's life.

7831005
I'm fairly certain Celestia is strong willed enough to continue holding her country together despite her sister's apparent death. That would mean most events would play out the same as everyone else wouldn't know the difference.

Maybe she would be more depressed and be a less effective ruler. Maybe she'd take it in stride and try to ensure nothing like Nightmare Moon could happen again. There is a slight chance that without the hope of her sister's return, Celestia could fall apart, but I don't think that'd happen.

Celestia would soldier on, feeling guilt, but taking solace in the fact that if she hadn't done what was necessary the world would suffer. It'll be an old wound that never quite heals, Cadance will probably be treated with significantly more trust and familiarity, Celestia seeing a chance to regain her lost sister in a way. The tale of Luna and Nightmare Moon will probably be much more prominent, but altered to imply the Nightmare was an outside force that struck her sister low. A way to memorialise Luna without tainting her memory. There will be plays and novels depicting Lunas fall to a demon, she'll become a romantically tragic character, a noble Princess brought down barely into her reign.

7831011

Remind me, for what reason at all, has the Luna turned into a Nightmaremoon?

7831025
I assumed that if Luna was blasted by the Elements, she was Nightmare Moon. It does seem like the question stated talks about how Celestia thought she accidentally killed her sister while trying to reform her.

What if, Celestia didn't know that the Elements simply banish her?

If Luna wasn't Nightmare Moon and Celestia thought she killed her, her reaction would likely be way more negative. It's one thing to accidentally kill your sister when she is trying to end the world through eternal night, it is quite another when she is valiantly fighting something by your side and you catch her in the cross fire. That would probably destroy Celestia completely.

Celestia never wanted to kill Luna, but she didn't want to be killed herself, which is she just banished her even though she didn't like that either.