How do you color the whole issue as him only resigning, when three board members quit over his presence there. That's a lot of pressure from the company.
It looks an awful lot like coercion...
But, isn't it up for him to sue if he feels he did not resign voluntarily? It seems like he probably would not do so.
The problem is, the CEO's job is to be the figurehead for the company. He's not the President -- he's not in an operational position, his sole job is to represent the company to the board and the public. His inability to do so effectively is absolutely grounds for removing him. Its a fine line to walk when you get arcane labor laws into the picture, but the fact is, with the uproar he wasn't capable of doing the singular thing his job exists to do. If he was the President of the company, I doubt he would've been pressured to resign. (Its very much like the laws against things like weight or sex discrimination -- when someone's job is specifically related to their fitness or gender, its been shown repeatedly that laws like these don't apply.)