So if Sullivan doesn’t give them permission to drop the case, what can he do?
How can he force the DOJ to prosecute the case?
Can he, in essence, prosecute it himself, by just declaring Flynn guilty and sentencing him?
Evidently the DOJ railroaded Flynn and got him to plead guilty through coercion by threatening to prosecute Flynn's son.
Then Flynn, under penalty of perjury, made statements admitting his guilt. Sullivan could consider contempt of court or refer him to DOJ for perjury charges. The latter won't work but the former might.
The real question might be "what will Sullivan do about the DOJ misconduct?" The appeals court might order a new trial for Flynn, followed almost instantly by the DOJ dismissing charges before a different judge.