I think they'll reverse. The clause used is for serious situations like attacking Fort Sumter with arms. Plus, there's been no trial, and given the rights at issue, if it's arguable that he's not an insurrectionist, which it is, the court should defer.

The court will not touch whether or not he is actually an insurrectionist. It will be a purely procedural decision.

The court may admonish the state court though to make sure others fall in line. It may, in the alternative, reverse with a short decision — this can also have the effect of saying "you're an idiot, and I don't have time for you," amongst jurists.