Even if that client were to pay (and they're probably not inclined to send money to the firm), what's to say that the CEO won't keep it all as their own "back-p

Even if that client were to pay (and they're probably not inclined to send money to the firm), what's to say that the CEO won't keep it all as their own "back-pay"? I would contact an employment lawyer so that you'll get your 2+ months of pay, turn in all company materials and data, and leave on Monday morning.