> Unclear how to value the equity I gave up, but it probably would have been about 85% of my family's net worth at least.

Percentages are nice, but with money and wealth absolute numbers are already important enough. You can leave a very, very good life even if you are losing 85% if the remaining 15% is USD $1M. And if not signing that NDA will help you landing another richly paying job + freedom to say whatever you feel it's important saying.