You do have to respect the terms of the deal. That being said, here's what I would do: 1) Fire him. Co-founders can be fired, and you and the other partner have majority vote. You wouldn't owe him any money because he hasn't worked since you stopped paying him.

2) Decide a fair company value and buy his equity stake. This guy is clearly a distraction and the best thing to do would be to completely cut dies and free up equity.