Maybe even because holding him accountable now can give him a chance to learn if that is possible before it is too late and he does something he will regret forever.
I doubt he will listen to any reason and I doubt he will regret it forever. A person without empathy (pathological narcissist) which the OP believes he is has no self doubt. They will destroy you, feed off your hurt, enjoy your distress, find it funny.
The best thing to do is get away and make a life of your own away from this toxic mess.

Holding on endlessly, hoping for change, that he will 'see the light' is damaging, exhausting and a waste of time.

I have a vicious sister who seems to hate her siblings. Trying to talk to her and hold her accountable is hopeless, it just makes her indignant (how dare you) rage and attack.
She was narcissistic mother's favorite, the one who could do no wrong.