Harry and Ron would probably be very worried. They'd rush to her side immediately. Harry might use his skills to try and find a way to heal her quickly, while Ron would be freaking out a bit but also trying to be helpful.
Another aspect is Draco's reaction. He may be used to seeing Hermione as an adversary, but when he's injured by her, it changes things. He might feel a sense of betrayal, especially if he had started to see her in a different light before the incident. In some fanfictions, he has to deal with physical pain as well as the emotional turmoil of being hurt by someone he thought he could trust, at least on some level. This creates a complex web of emotions that fuel the angst in the story.
One possible fanfiction could be 'The Unforeseen Consequence'. In this story, Hermione accidentally casts a spell during a duel that seriously injures Draco. It then delves into the angst as Hermione is filled with guilt and Draco has to deal with his newfound vulnerability. The author does a great job of exploring their complex relationship in the wake of such a tragic event.
One great fanfiction with Draco and an injured Hermione is 'Healing Wounds'. In this story, Hermione gets injured during a battle in Hogwarts. Draco, surprisingly, steps in to help her, and their relationship takes an interesting turn from there. It's full of drama and some really sweet moments between them.
One great fanfiction with this plot is 'Slytherin's Compassion'. In it, a group of Slytherins come across an injured Hermione in the Forbidden Forest. They initially have mixed reactions but end up helping her. It shows a different side of the Slytherin house.
One idea could be that Sirius uses his knowledge of magic from his time as an Animagus and as a member of the Order to quickly heal Hermione's injury. Maybe he transforms into his dog form to track down any threats still lurking around her.
In some fanfictions, Hermione gets injured in the Forbidden Forest. Maybe she's exploring and stumbles upon a dangerous creature or a dark magic trap. This kind of plot allows for a lot of adventure and mystery. It also gives the author a chance to show how she copes with the injury in a dangerous and unfamiliar environment. And sometimes, she gets injured in a magical accident in the library while researching some dark magic, which can lead to all sorts of interesting consequences and character development.
One common theme is friendship. When Hermione is injured, it often shows how Harry and Ron (and other friends) rally around her. For example, they might drop everything to find a way to heal her or protect her from further harm. Another theme is her own strength. Even when injured, Hermione usually shows great mental fortitude, like in fanfics where she continues to study or help others despite her pain.
It could also be that they are working on a new spell together in Snape's private laboratory. A miscalculation in the magic could lead to an explosion or a backfiring of the spell, causing them both to get injured.
Ron would be devastated. He might initially be at a loss for what to do. But then his Gryffindor courage would kick in. He'd start researching every possible cure or treatment for her injuries. He'd be the one to comfort Harry and the others while also being the most vocal in demanding justice for Hermione. His relationship with Hermione, whether you see it as just friends or something more, would make him act in a very passionate and protective way.