It is unclear whether this opinion would also hold that one may not forgive the judge who received a bribe from returning it. If this opinion extends to bribes as well, a judge would be obligated to return a bribe even if it is not requested of him. The Kitzos (C.M. 9:1) rules that according to this opinion it does apply. Therefore, according to this opinion, a judge is required to return a bribe even if it is not requested of him.
The Ritva, in Baba Metzia 61a, offers this explanation on the opinion that states that one may not forgive his lender the interest payment: We derive that one must return interest payments from the pasuk, “v’chei achicha imach” (Vayikra 25:36). The Gemara says that this obligation only extends to the one who received the interest and not to his heirs. If one dies after receiving interest on a loan, his children are not required to repay the borrower. (Generally, heirs must repay any debt that the deceased had from the estate that they inherited.) However, they are not obligated to repay interest payments that the deceased was to return. This is because returning interest payments is a mitzvah that the Torah only wanted the lender to do. Therefore, this debt cannot be forgiven by the borrower since the Torah wants him to carry it out. Based on this we can assume that, regarding returning a bribe whereby we do not find the same specific requirements, all would agree that the bribe may be forgiven and as a result a judge would not be required to return a bribe unless it was demanded of him.