Thus:
Option #1: Just quit, and keep your mouth shut. Do you really want to be party to a fraud? And, given it is a fraud, will your equity ever actually be worth anything? This is the easy option.
Option #2: Quit, tell world you think this is fraud. Better talk to a lawyer first, you want to phrase it the right way (and may get sued anyway).
Option #3: Stay on, try to convince them it's bad idea. In this case I'd go for "I think this is fraud, it's too risky", with nice broad paper trail that will be trivially findable by discover if they get sued later, and copies of paper trail kept by you. You may well get fired. And do you really want to keep working for these people?
Thing is, if company's choice is "fraud or bust", it's dead anyway. So you're not losing anything by quitting (and maybe you can get them to pay you a lot of money for transition to replacement CTO.)
If you do quit, leaving behind the nice paper trail for lawsuit discovery might discourage some bad behavior.
(Not a lawyer. Not legal advice. I'm random person on Internet. You probably want to talk to a lawyer.)