If the Senate convicted Trump with the effect of banning him from future office Trump would have the right to appeal on the ground that Congress exceeded its Constitutional power in convicting him after he had left office, and the SC would rule on the question.
Supreme Court already ruled that there is no right to appeal. Nixon v. US, the Supreme Court ruled unanimously that when the Constitution said the Senate had sole power, it meant no appeals.
I am completely serious when I say that an appeal to the Supreme Court is going nowhere. We are used to other parts of the system, where the Supreme Court is the final arbiter. This is one of the exceptions to that.