Fan Casting Dr. Adrian Chen in Batman: Arkham Asylum

When the Blackgate inmates took over the Medical Facility, Dr. Chen was in the Surgery Room. The inmates had strapped Chen into a chair and tortured him to set him as bait. Batman then appeared and Dr. Chen told him it was a trap, to which Batman replied: "I know, just not for me", before he beat all the thugs and released him. Chen then went and sat into a chair, and thanked Batman. If Batman returned to see Chen in the Surgery Room, he's not there. Presumably, he went and found a place to hide out the remainder of the Joker's riot. Alternatively, he could have found a way off of Arkham Island, though that was unlikely.