Why did they keep Castor Troy alive?
After they took Castor's face off to put on Sean's body, they no longer needed to keep Castor alive. In fact, Sean thought Castor was dead and was shocked to see that they were still keeping him alive.
At the very least they could've lobotomized Castor so that if he had ever gotten out of the coma (which he did) he would basically be brain dead.
You must defeat Sheng Long to stand a chance.