[wpietri]

My general answer for people asking this question is: when you think you can sustain yourself. And it sounds like you're almost there.

It sounds like the question for you is whether you can find new clients at a rate fast enough to replace old ones. This is a question you'll never be able to answer fully as an employee, because employers generally don't like you putting out an "open for business" sign. So in your shoes I'd put together a marketing/sales plan, take the new customer, and devote some time over the next N months to seeing if you can build up enough interest and leads that you will have plenty of work down the road.

It sounds like the worst case here is that you get to the end of your contracts and have to go get another job again. Which is not a terrible outcome as long as you don't burn your bridges. And it's worth noting that after a period of freelancing you may decide you'd rather have a job anyhow, so you can look at the next months/years as an experiment not just on prospects, but on whether or not you will be happy with it.