You can take this case to the governor if you want, but you might have more luck pushing the case with the local AG.
Personally, I'd push for assault with intent to commit mayhem if the AG stands firm on no charge for attempted murder. (Besides, attempt to commit mayhem carries a heavier penalty in most states.)
I am relieved to read your son is recovering, and feel terrible for what he and your son went through.
That sure sounds like attempted murder to me! The prosecutor could be going after a lesser charge for lots of reasons. Maybe they think the effort and resources going for attempted murder would be too much, perhaps their caseload is overwhelming and they need to prioritize. Sounds awful but sometimes that's the situation. Or maybe they think the standard of evidence for attempted murder would be too difficult to prove, putting the case at risk.
I like your idea about contacting people to see what you can do, AG or governor. Hope you get some good advice and get a good result.