In all likelihood, the second the kid shows up with an attorney in tow, the school board will consult with their own attorney, apologies will be offered, and the idiot principal will be reeducated (preferably in a camp in Siberia).
Unfortunately, they're just as likely to bring the house lawyers in, dig in their heels, and wait for the kid to graduate and it not to matter anymore.
School boards have time on their side. This kid is a senior, so he's going to graduate in a couple months. Once that happens, how much money are the parents going to spend chasing after this? This is why the principal is threatening the suspension and loss of extra curriculars - that tends to include graduation ceremonies and prom night. Why threaten lawsuit when you can just say "nope, you don't get to walk the stage with your peers. Shoulda respected my authoritah." And by the time the appeals get done, it won't change the fact that he missed the event.
And the update on the article, while completely ditching the BS "I'ma gonna call the IRS on you" line, is apparently now claiming that he's in trouble for using school equipment to post non-school work. Which would seem to imply that if he takes the memory card home and uploads them from his personal computer, they don't have a concern? (Which leads to: how do you tell the difference?)