Any rational person would want his ex-wife as far away from this court case as possible since the disclosure of his infidelities comprise a central tenet of his claims of defamation. To compound the matter further, she voluntarily disclosed this information in addition to a lot of the context behind it to parties outside the marriage.
He may think she could testify to the amount he earned or the veracity of the Marko emails, but at what cost? He’s exposing her to a blistering cross examination which would invalidate most of his other claims (I.e. patrons quitting because he cheated on his wife, his reasons for going to Thailand). The letters she released could also be entered into evidence and she could be deposed on the contents of those and why she sent it to other parties.
Does he not realise that her testimony is only going to make him look worse and that his claims of defamation were actually based of factual information?