I hate to say it, and I know it's going to sound fatalistic, but her decision is very likely going to stand.
Clarence Thomas literally handed her this argument on a silver platter. And say what you will about him, the legal system still considers him one of nine justices of the highest court in the land, and his words still carry that legal weight.
If Jack Smith appeals, there's (IMO), a 50/50 chance he wins on appeal. I could see the appeals court using things like logic and rational thought, kicking Cannon off the case and reinstating the charges against Trump (Or however that would work in the legal sense). But I could also see them saying that since she was merely following what Clarence Thomas told her to do, her decision is on sound legal footing, would most likely survive Supreme Court scrutiny, her decision was proper based on the SC ruling, and the decision stands. And from a strictly legal standpoint, they'd be right in doing so.
And if this case were to make it all the way up to the SC......since Cannon was literally following their blueprint, there's 0% chance that they'll suddenly rule against her. Nothing good can come out of appealing to the Supreme Court, and in fact it may be exactly what this supreme court wants and why Clarence Thomas added that little tidbit into the decision, so the SC can rule that all special counsels are illegal and the entire J6 investigation was unconstitutional as a result.
(Of course, Hunter Biden's conviction will still stand, because reasons.....)
This case is dead. The other three are on life support, and the doctor has already called for the chaplain to deliver last rites.