Gyno can reappear in some cases, there is no denying in that. Zupperman did have this issue. However, for most people who take their anti-gyno treatment seriously, this will not be an issue.
You have to understand, there are guys here who get on a 2 months letrozole + nolvadex therapy, get rid of their gyno; then they jump on a cycle with NO anti-Es - then come back and complain they got gyno again