What are the chances of degree revoke if an unrelated plagiarized paper was published during the course of Phd studies The Phd Thesis and course work all are un-plagiarized; degree completed through all the normal procedures of the university.
However, a plagiarized research paper which is un-related to the doctoral thesis and coursework was published during the PhD tenure.

What are the chances of degree revoke (the degree has long been granted).

Regards.
It can happen.  But it would depend a lot on the policies at that institution.  As reported in the New York Times, consider the case of Senator John Walsh (D-MT), whose master's degree from the US Army War College was revoked when it was discovered that he had plagiarized a paper he'd submitted in partial satisfaction of his degree requirements seven years earlier.  They even ground his name off the bronze plaque listing the school's graduates.