Thanks qbteachmt,
By the way, through the years, I always enjoyed your replies and posts.

"...For a Schedule C cash basis taxpayer, there is no entry for the missing part of gross income, so there is no entry for the unpaid income as a loss".

I was told check on Schedule C; an entry under "Returns and allowances, ". 
My client supposed to get a 1099-NEC at the end of the project. Ipso facto he is a contractor
The first 3 months of work were worth $25,000 that were never paid because of the sudden bankruptcy. 

At first, I doubted that the $25,000 can be allocated under "Returns and Allowances"; this is why I checked the Community.
It boggles my mind though, that three months' work, is just going to be whipped out and gone and nothing can be deducted on the return.