In some fanfictions, his fall off the broom could be a turning point in the story. It might lead to him discovering a new magical ability. For instance, he could unconsciously use a form of magic to slow his fall or even levitate himself slightly. This newfound ability could then be explored further in the story, perhaps making him a more powerful wizard in unexpected ways.
He could get seriously injured. In some fanfictions, he might break a bone or two. It would also likely lead to him being out of the Quidditch match if it happened during one.
In certain fanfictions, Harry's fall could be a part of a larger conspiracy. Maybe someone tampered with his broom on purpose. This would then lead to an investigation, with Harry and his friends trying to figure out who was behind it. Along the way, they could uncover other secrets about Hogwarts or the wizarding world in general, which would add more depth and complexity to the plot.
Dumbledore could also be a savior. Given his powerful magic, he could easily appear at the scene and use a spell to stop Harry from hitting the ground too hard. Or perhaps one of the teachers at Hogwarts, like Professor McGonagall, who is strict but caring, would use her transfiguration skills to create something to break his fall.
He might get injured, like break a bone or get a bad bruise. Then he'd have to go to the hospital wing at Hogwarts for treatment.
In fanfiction, Naruto might discover a hidden power or ability when he falls off the cliff. It could be something related to the natural energy around the cliff area that he manages to tap into during the fall, and this new power could help him in his future battles.
A plot twist could be that when Draco falls off his broom, instead of Hermione helping him directly, she uses a spell to make his broom catch him at the last moment. This shows her intelligence and also makes Draco question her motives. Later, he discovers that she didn't want to expose their growing friendship to others. Another twist could be that Draco's fall was actually a planned thing by someone who wanted to harm him, and Hermione has to figure out who it was while taking care of Draco. This adds a mystery element to the story.
Well, he could encounter all sorts of supernatural beings in Mystic Falls. Maybe he'll meet vampires and use his magic to either protect himself or try to understand them. Since he's used to dealing with magical creatures in his own world, he might approach the vampires with a mix of caution and curiosity.
They might be using the broom to visit a distant relative. As they fly, they could encounter different magical creatures and landscapes. Draco could be excited to see new things, while his dad might be reminiscing about his own travels. This would show the bond between them as they share these experiences on the broom.
Maybe it was a jinx. In the wizarding world, there are many spells that could make a broom go haywire. Some jealous rival in a Quidditch match could have cast a spell on his broom to make him fall.
Peter might fall off the mountain due to being chased by a powerful villain. As he falls, he could be thinking about how he got into this situation and what he could have done differently. When he hits the ground (assuming he survives), he has to quickly recover and find a way to defeat the villain who caused his fall.