... This accountant is a casual friend and we have played golf together, his wife that passed 4 months ago was my wife very good friend. ...
The passing of his wife certainly could have contributed to some mistakes. He's grieving (maybe very deeply, even/especially? if it doesn't show), and that could lead to concentration gaps, missed opportunities, etc.
Of course, none of that changes the effect it had on you, you need to deal with the fallout, but it might help you emotionally to look at some explanations for what happened.
Which leads me to another point - I'm wary of doing business with friends/family. There certainly can be advantages to doing business with an individual, but there are also the downsides of not having a backup when problems arise, no one else to even answer the phone emails, etc.
... Should we sue him? Or move on .
Probably neither. As others have said, you really need to understand the
true monetary damages (which is not the tax estimate delta). Making moves that resulted in higher taxes, if proven to be negligence on his part, maybe could be claimed (which may cost you more in lawyers fees/time that what you can get). Maybe money lost in liquidating more than you expected, and raising this year's tax bill, or other costs associated with that? But if those costs were just accelerated rather than eliminated, the damages will be less, and maybe not worth pursuing.
No way to know until you get it sorted out with the other CPA. But if there are definable damages, I suspect that other than asking that he return any fees you paid him for this apparently sub-standard work, I doubt that any other action will be worth the time/effort/costs. Maybe he will offer to reimburse you for more than that. But if not, and after considering the alternative, then yes - move on.
-ERD50