Ask HN: client offers to pay with income, should I take it?

I have been working with a client for 9 months now on a saas project. we did a fixed price project and I delivered a product that is almost ready for sale. The client has 3 big leads and is finalising the sale with them (I attended the meetings) He ran out of money and suggested a 3 year contract where I will be paid x per customer in return of 3 months of work if those 3 leads close, I can get almost double on my investment (lost time and revenue).

How should I evaluate this deal?