The thing that I've encountered as a teacher in public middle and high schools is that even when you hand the parent concrete evidence of a transgression (for example: printed evidence from the web of plagiarism, or a bag of the weed taken from their locker), the parent will look you straight in the face and say, "My kid didn't/wouldn't do this. I raised them better." Someone else is always to blame, and it's usually the person who dared tell you that your kid's not perfect, because how dare you?
I doubt that these kids will be punished in any meaningful way. Instead, the school district will make a plan to do something stupidly expensive and over the top and it won't go anywhere except to the news where they'll say they're "working on it."
As for the others on the bus? They're the ones we need to work with from a young age to make them understand that their response shouldn't be "it's not my problem" or "I can't do anything." All the time in the news and in media (TV, movies, books, etc), we see the perspective of the bystander who later wishes they'd done something. It's not the bullies we have to find and eradicate young, it's the bystanders that we have to empower, because that's a strength of character that will never go away and is sadly lacking in society today.