Actually, Skilling doesn't need to overturn all 19 convictions to regain his freedom. By now he's served his sentence for all but two of the securities fraud convictions. So if he gets those two (or more logically, all 12 of the securities fraud convictions tossed), he would go free while the government decides whether or not to retry him. If he is retried, he'd remain free until re-convicted.
If Skilling wins a reversal of the conspiracy count, he will challenge the securities fraud counts by making this argument:
Ex-Chairman Ken Lay and not Jeffrey Skilling committed securities fraud. The jury convicted Skilling of securities fraud only because it found Skilling and Lay co-conspirators. Thus Skilling -- like co-conspirators in general -- could be convicted of Lay's conspiracy-related crimes even if Skilling didn't participate in them. Since the conspiracy Skilling was convicted of -- honest services -- is invalid, it can't be used to tie him to Lay's crimes. (Ken Lay died before he could appeal his conviction, which voided it.)
Arguing that Skilling's convictions should stand, the government charges that overwhelming evidence proved beyond a reasonable doubt that Skilling committed securities fraud -- that is, the jury found the crimes were not just Lay's. For that argument to win, the government must show that, given the evidence presented at trial, no rational jury would have acquitted Skilling of securities fraud. The government could also win if, to convict Skilling of honest services fraud, the jury also had to find all the facts necessary to convict him of securities fraud, so that convicting him of the former meant the government had also proved the latter.
A decision won't come for weeks or perhaps months -- and that decision might not be final, as the loser could ask the Supreme Court to weigh in again, which it could agree to do. Even so, the decision at this stage will have powerful consequences not just for Skilling but also for other defendants pursuing appeals of honest services convictions.
Prior to today's argument -- at which the judges will get to ask questions and perhaps tip their hands about how they view the case -- the only indication of the court's view came in its Sept. 3 decision to deny Skilling bail while this appeal was pending.
On the one hand, denying Skilling bail could suggest the court isn't ready to void the securities fraud convictions, as those are the only ones still keeping him in jail. Moreover the arguments Skilling made in favor of bail are essentially the same as he is making on appeal.
On the other hand, the court didn't explain its reasoning in denying bail. It's possible, for example, the court was just concerned Skilling would flee while it was making up its mind. Nonetheless, in arguing over bail, the government conceded Skilling wasn't a flight risk. Still, the government -- and all the Enron victims who want the convictions to stand -- can't rely too heavily on the bail-denial tea leaves. All the arguments haven't yet been made, and the court hasn't had time to consider them. After today, however, the arguments will be done.