Harry hade inte en profetisk vision. Det var bara hans fantasi.

Du verkar vara förvirrad över vilken sorts "vision" som Harry hade. Här är den aktuella passagen.

"It's not easy, Apparition, and when it's not done properly it can lead to nasty complications. This pair I'm talking about went and splinched themselves."
Everyone around the table except Harry winced.
"Er - splinched?" said Harry.
"They left half themselves behind," said Mr Weasley, now spooning large amounts of treacle onto his porridge. "So, of course, they were stuck. Couldn't move either way. Had to wait for the Accidental Magic Reversal Squad to sort them out. Meant a fair old bit of paperwork, I can tell you, what with the Muggles who spotted the body parts they'd left behind..."
Harry had a sudden vision of a pair of legs and an eyeball lying abandoned on the pavement of Privet Drive.
(Goblet of Fire, Chapter 6, The Portkey).

Som Harry Johnston påpekar, var detta inte tänkt att beskrivas som en profetisk vision. Om du kommer ihåg, har Harry aldrig någon stor förmåga alls för Divination eller förmögenhet i böckerna. Han förutspådde inte framtiden. Han lät sin fantasi springa vild och försökte bilda vad efterföljningen av en Splinching kan se ut.

Visionen i detta sammanhang avser

a vivid mental image, especially a fanciful one of the future.

plural noun: visions

"he had visions of becoming the Elton John of his time"

snarare än

an experience of seeing someone or something in a dream or trance, or as a supernatural apparition.

"the idea came to him in a vision"

(Google dictionary).

Därför kommer "Visionen" Harry aldrig att ske i de senare böckerna. Det är bara en bild som tillfälligt kommer in i Harrys sinne.

Splinching som ett begrepp ingår emellertid i berättelsen. Ron blir splittrad.

The moment his eyes fell upon Ron, all other concerns fled Harry's mind, for blood drenched the whole of Ron's left side and his face stood out, greyish white, against the leaf-strewn earth. The Polyjuice Potion was wearing off now: Ron was halfway between Cattermole and himself in appearance, his hair turning redder and redder as his face drained of the little colour it had left.
"What's happened to him?"
"Splinched," said Hermione, her fingers already busy at Ron's sleeve, where the blood was wettest and darkest.
Harry watched, horrified, as she tore open Ron's shirt. He had always thought of Splinching as something comical, but this...his insides crawled unpleasantly as Hermione laid bare Ron's upper arm, where a great chunk of flesh was missing, scooped cleanly away as though by a knife.
(Deathly Hallows, Chapter 14, The Thief).

Liksom Susan Bones.

Not until the fourth [attempt] did anything exciting happen. There was a horrible screech of pain and everybody looked around, terrified, to see Susan Bones of Hufflepuff wobbling in her hoop with her left leg still standing five feet away where she had started.
The Heads of Houses converged on her; there was a great bang and a puff of smoke, which cleared to reveal Susan sobbing, reunited with her leg but looking horrified.
(Half-Blood Prince, Chapter 18, Birthday Surprises).

Det är uppenbart från dessa beskrivningar att Splinching är en hel del mer smärtsamt och farligt än Harry föreställer sig. Hans idé om Splinching är inte korrekt; Det är bara en ledig gissning på vad det kan medföra.