Assuming that is so, in concept, Garland could attempt to remedy the defect by the appointment of a new qualified prosecutor up until a jury has been seated. At that point the invalid appointment defect would probably be constitutionally fatal to any prosecution because double jeopardy attaches once a jury has been seated.
In addition, the lack of validity to Jack Smith's appointment would provide a legally and politically compelling argument in favor of a new Trump AG voiding all the federal prosecutions. Moreover, the invalidity of Jack Smith's appointment would help open him, Garland, Biden, and others up to criminal prosecution and civil liability.
My guess is that the lawyers and parties know this, but the legal gamesmanship is too complex for explanation to the general public. That will change if Thomas or another Justice addresses the issue in an opinion, even in a concurring or dissenting opinion.
Indeed, the Court itself could order the issue to be formally taken up by the parties in the current case and thereby gum up the works. Or, the Court or Thomas or another Justice could point out the invalid appointment problem in a way that forces it to be dealt with by the parties and the trial courts.
In any event, if given credibility at the Supreme Court level, the invalid appointment problem would be not just a legal bombshell but also a political one. As it is, a new and valid special prosecutor from among the ranks of current appointed and confirmed US Attorneys will be virtually impossible to recruit.
The legal, factual, and political problems now apparent with the federal cases against Trump would make anyone new to them with a lick of sense decline such an appointment unless they are given full authority to void the whole thing. I do not see such an appointment happening unless Jack Smith is to be made the fall guy for the whole thing. If so, my guess is that Smith would eventually talk and put Garland and Biden in the soup as to liability for civil and criminal conspiracy and other charges and claims.
From that perspective, the Court's impending ruling on official immunity will be of considerable personal interest to Biden, Garland, and Smith. After all, they have much to answer for as government officials.
If Jack Smith gets ousted, Merrick Garland will just get loaner prosecutor (persecutor) Matthew Colangelo back from Alvin Bragg’s New York show trial.
Thank you for this splendid analysis.