A couple points:
1) I think everyone can agree, that whether Vanoli's actions were legal or not, has very little relevance to whether the operations he conducted are binding. If they were indeed illegal, he can go to jail, and the operations he transacted may very well still be binding.
There might be cases where it can be proven that the buyer acted in bad faith, but that is a very high bar and an uphill battle to prove.
2) We are talking about stability of Argentine institutions, but not of the judiciary per se. This is a commercial transaction, and default is an option. That's how futures contracts - how all contracts - work.
3) With regard to the trust issue, the question is "next time there's a trade, should I worry about being screwed or not". There is a case to be made that enough players will buy the argument that this particular default, should it happen, is not a precedent for general stability, viz. that the operation in question was less a commercial transaction than a dirty power play, one that made no fiscal sense, one made with the clock ticking down, and that most buyers had to know this. These trades were taking place here, not in New York, and everybody involved had to understand the implications, unless they were imbeciles: billionaires but imbeciles.
4) No default has actually taken place yet. The position Sturzenegger is taking is is an initial one from where to negotiate - a nuclear option, if you will. Possibly the point is to make the actual buyers come out of the woodwork. Possibly there is a middle ground that can be found, where buyers who can demonstrate good faith will have the contracts honored to a greater extent than those where bad faith can be demonstrated.
I do understand the alarm, but there are very few good solutions for this. Again, this (the sale of these futures contracts) is all a play with 2019 in mind, and these traps were woven well.