We are perhaps conflating symptoms of the blackmail - with dementia.
"He's terrified". If he's terrified, perhaps the process has been lasting for quite a while (perhaps not). But I think if he has been coerced to carry on actions that go against his will (and humanity perhaps) - he would be developping trauma. After a while, without solutions, and being forced to go against one's own "direction" - things can become difficult.
I am not an expert in the field, but a skilled psychologist may be able to lay down a basic idea on the damages of blackmail, on the personality.