Do you really think sending a few scapegoats to prison will solve anything? The problems are systemic. Some faces may change but the agencies remain organized and financed the same way.
While there are certainly people at the top that need to go to jail (and it obviously is an open question as to who and how many), I strongly suspect that many of the people working there are simply following vague or seemingly-unrelated orders. Also, cries of urgency and need are hard to ignore, especially when they are wrapped in patriotism and the idea that you're trying to protect others.
All of this is especially true at the NSA, which is historically very compartmentalized ("need to know"), which further confuses the issue.
As for the future once those responsible are jailed, vigilance is the price of peace. In this case, what would be making sure regulation/oversight happens and actually has the power to do their job. The problem of regulatory capture is the systemic problem across the government in general. We need to address that problem (urgently), but it is not an NSA specific problem.
I don't think the threat of prosecution would, actually, for several reasons. But it any part of the government was willing to uphold the law, it might make people think twice, that maybe following illegal orders isn't patriotic after all.
Even amongst the Nazis, most high level people had compartmentalized knowledge that was only evil when combined. Indeed, the subtitle and thesis of the book reflects that: "on the banality of evil."
Her theory is that unethical organizations can structure themselves in such a way that almost nobody is actively breaking the law.
Hardly surprising the organisations that employ them feel they're above the law.
The U.S. Army feels that it is above the law?