I do not think they would have allowed him to fight KlitschKO if had been sick. Chagaev was not sick in any medical sense. I do not see a point in discussing something that numerous doctors has proven. Chagaev was not sick and he was the real WBA champion. His title was stolen foully by corrupt promoters leading by their greed.
If you actually bothered to research subject little bit, instead of inventing fancy conspiracies you would see that he indeed was sick in medical sense. Different matter is should he be allowed to box with hes condition. Finnish boxing commission along with vast majority of world boxing commissions dont think he should, because of the risk of him contaminating other boxers.
I am afraid that you did not bother to research the subject a little bit. Chagaev was ot sick in any medical sense. I would recommend you google on this subject.