Michael may be a guy who just gave up hope, or he may be an evil jerk, but that doesn't change the fact that Terry's cerebral cortex is filled with spinal fluid.
That is an "assumption"....not fact, because it can only be verified by having an MRI ......which Michael would not allow. If it were....."filled with spinal fluid", Terri would NOT have any awareness of her surroundings nor have any ablility to talk.