Thanks for adding some detail.
PubPeer.com did not create this controversy. They only provided the platform for others to use to "peer review" scientific papers (from elsewhere, anywhere) and to discuss controversies in scientific and academic conduct/misconduct.
I agree. PubPeer is in the midst of the controversy simply because they don't want to disclose information identifying posters. Apparently they are resisting a subpoena.
I am ignorant of the bible and am want to intentionally misrepresent the intent of its scripture and thus I am on my way to hell because I am an atheist, commie, fascist pig with ugly thinning hair and bad breath - in order to track her down and SLAPP her silly should I sue Percy to get her name, address, phone number?
That probably would not reach the level of actionable defamation. However the level of insult that constitutes defamation is much lower when the subject matter is accusation of committing a crime, immoral acts, capability to perform one's profession, or having an odious disease, or dishonesty while performing one's profession.
What if she claimed to have information about you giving herpes to a 15 year old and her claim resulted in you getting fired from your job as a teacher? What if that claim was completely fabricated?
That said, the comments as you describe them seem mild and probably not defamatory.
Like Dr. S, I would be pissed (sorta) but is that Percy's fault?
I don't think that's even the issue. A subpoena to provide information about a third person does not cast any blame on Percy.
Seems to me the new school may be liable for breach of their employment offer (iffy) and the anonymous e-mailer may be accused of libel (again, iffy).
I suspect that the offer letter would have left an out for this kind of mind change. Any competent lawyer would have advised doing so.
Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)
I have never met a man so ignorant that I couldn't learn something from him. Galileo Galilei
If there is no struggle, there is no progress. Those who profess to favor freedom, and deprecate agitation, are men who want crops without plowing up the ground, they want rain without thunder and lightning. Frederick Douglass