Did you take equity or a promise of equity? If so, flat out ask how things are REALLY going.

If you're just taking $ for hours and you like the work, stay for as long as they keep paying you but still ask if there are any problems. If they punt and don't answer or you don't believe they're being honest with you then start looking at your options for getting out of there.

You have to know that they'll drop you as soon as the cash runs out, so you owe them NOTHING.