@BulldogTom I do feel for you. One of the hardest things I had to learn - and I have to keep RE-learning it every couple of years, is that I can not allow myself to care more about my clients' finances and tax situations than they care themselves. We know how to fix it - if only they will listen! Their lives could be so much better! But many if not most if not all will not listen.
So instead, concentrate on "Let not your hearts be troubled." Note that at some level we allow ourselves to get all worked up; stop it. (Lecturing myself at least as much, maybe more, than you.) You did your best; the client screwed up and it's not your fault. Do not let your heart be troubled. And charge him a big fat fee - up front - if you take on trying to get even some of the mess fixed.
Plus hugs to you. Not Rita hugs! Sympathy hugs.