This is the right call: "c) Plan on 3 years back taxes to get him in good stead."

I've done a few of these. One, it did destroy the relationship, but I was upfront about the discovery and its potential impact. The spouse took it as a complete personal affront, since she was the one who had been trying to maintain the records all the years, but had done so with no guidance. Also, I tried to make a referral to a CPA I love and send lots of people to, and they reported to me they had already turned this couple away years ago. There's no shame it it being beyond your interest or ability or outside of your practice. By passing on it, you are not making it worse.

And definitely get paid ahead.