They should have took this one then and put it to rest for good.
It was never very likely that the Court would take this case. This case reached the Court as a case that weighed freedom of expression against concerns about violence. There is a long line of cases that grant schools pretty broad powers to restrict student speech if they do so in the name of preventing violence. The current Court has never shown an interest in overturning that line of cases, so the most likely result in this case was that the Court would just let the appellate decision stand without taking on this case.