This was the line that got me too. Fitz had no legal right to prohibit Armitage from telling anybody what he had done in the matter, nor had Armitage any obligation to follow Fitz's illegal "order." Armitage has proved that he is an immoral, untrustworthy person and will never again have any credibility. That, apparently, is all the punishment he will get. But Fitz has done much worse. Although he has been accused of prosecutorial misconduct on this thread, that is far too mild a condemnation; the man is a dangerous criminal who belongs in jail.
The Constitution provides for impeachment or expulsion of any government official therein named (i.e., executive, judicial, or legislative). Although it is silent on non-Constitutional officials, if the courts are looking for and finding "penumbras," here's one ready to spring into action: impeach the lying SOB for starters.
But it doesn't say that Fitz ordered Armitage not to say anything. It says he asked. Apparently, Armitage willfully complied.
Could Fitzgerald have granted Armitage immunity or would that have been made public?