I found myself in this situation back in 2008, not long after the crash. We had been working on a highly custom kitchen job for almost a year. About 6 months prior, the customer put the job on hold because he ran into problems with the GC doing sub-standard work that didn't meet code (our contract was with the owner, not the GC). We had approved drawings and were days away from ordering materials and cutting parts when the owner pulled the plug. Our terms were 20% on acceptance, 20% on start of fabrication, progress payments thereafter, so at that point, we had been paid for the work we had done, so I told him "Fine, let me know when you are ready to start again". After the crash, he got nervous that we would go out of business, so he asked us to refund the deposit, and promised that he would resume the job once things were settled with the GC, who at this point he was suing. I told him that we could maybe refund some of it, but that we had expended a lot of time on shop drawings, meetings, field measurements, cnc engineering, etc., and that any refund would have to be made in payments over time. His lawyer sent a demand letter the next day.
I get a lawyer, there is a back-and-forth, and we eventually wind up before a panel of lawyers in a pre-trial non-binding arbitration. At the time, I was using a paper calendar/organizer, and I had listed in there every meeting, every site visit, every day where I had set aside time to work on his drawings. The panel concluded that I didn't owe him anything, and that in addition, he was instructed to cover my legal fees.
They contacted my lawyer after to ask if I would still consider completing the job, since they already invested 20% in it. In the end, we completed the job and got paid in full.
The moral of the story is, don't take too much money in advance, and document the work that you do.