It sounds like the LLC is dissolving, so I would file a final LLC to protect your client from future liability for possible state fees.

In this situation you do the best you can. You and the client will sign returns complete to the best of your knowledge. 

I am semi retired now. When I was going full bore I had a ceiling that was sometimes used to help to develop the best knowledge we had. Be realistic and give it your best shot. Use the attorney to try to get real numbers, but barring that - use SWAG (Scientific Wild Ass Guess) based on prior year and what the client can provide. We can only do what we can do.. 

All of the numbers are on the ceiling over my head. When the client looks up it can give them inspiration. My side of the ceiling is clear. Everything on the return come from the client. 

BEST OF LUCK