I don't think it's that simple, even ignoring the difficulty of finding another job. I've been a software engineer for 10 years, and I've had to pull a few stretches of 55-60 hour weeks. Most engineers I know have done it; we don't like those periods but most of us really like our jobs overall.
In the OP's situation, I'd ask the boss to prove that it's reasonable to expect the company to become profitable under the proposed plan. Ask about dates, revenue, and customer commitments or at least verifiable customer interest. Make sure the boss considers the diminishing returns of working extra hours, and the need to recharge after a burst of extra hours. Working more hours can boost productivity for a while (depending on what you do), but not indefinitely. Personally, I can do 60 hour weeks for about a month before I become so sluggish and dumb that there's no point. Then I need a 4-5 day weekend and a return to 40 weeks for a while -- like 2 years. Cash helps too.
If the boss's plan is likely to work, I'd go for it. If boss won't do that, or tries and fails to be persuasive, start looking for a new job. The company is probably going to fail anyway.
If stock as payment comes up, don't accept it without doing your own research into the value of it. Startups are notoriously hard to price, and the manager may (honestly or not) be inclined to overestimate it.