In canon King Sombra's Horn remained intact after he was killed by Crystal Heart and possibly scattered to the winds. You could just dismiss the horn as being nothing but a horn I guess.

There's only one fan fiction I've read where something like this happens. But yeah, in a fan fiction or alternate universe anything can happen.

This is a gold mine for writers to use it as an Artifact Of Doom like the One Ring from LOTR.

Just like the One Ring King Sombra's Horn may drive crazy an unfortunate soul who found it. He may even be able to take control of the mind of Pony carrying his horn, through his mind control over the Pony he may even be able to somehow regain his physical body and power back and get his revenge.

1730485 In my universe, that horn contains Sombra's soul. Shining sends a team out and imprisons the horn in a case of crystal, but he can still talk to him.

In my headcanon, it's what keeps him alive, but he's unable to assemble himself for the moment. Ought to be a while before he'll come back. Years, even.

Yup. That's exactly what happens in my story, "Shade of A Crystal Empire." I know it's trope-y, but hey, if it works it works. Although in my story, despite it being an Artifact of Doom of sorts, his horn isn't the real centerpiece of the plot, at least past the first few chapters. It's just (half of) something that allows him to return. The real fun is what happens after he comes back.

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When you think about it, it's kinda odd they even left the horn intact like they did. Think about it, they didn't need to show the horn at all when he died but they did. Gets you wondering you know?

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Maybe they wanted to bring him back later on. Maybe as a ghost.

My Headcanon is that his Horn corrupts everything it touches and he was born with it and thats why he acts like an animal rather than a normal pony. Also I think that his Horn is rebuilding his body and wants to make him a new body made from crystals.

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Personally, I believe that (Since Meghan more or less confirmed him as a one-off villain and that he won't be coming back.)

I assume it's like how in a lot of media they show someone's decapitated head, piece of armor, weaponry, or other body part/accessory that either made them iconic or was important to them for dramatic effect.

Of course, I could be wrong-but, that's just my take on it.