generally, in situations like this, the IRS would say any loss is contingent until the final distribution is made. you don't know what your loss will be. at best you would have an estimate.
so it's likely the broker will report the proceeds but provide no cost basis. if so, report cost equal to proceeds. you'll take any loss in the year the final distribution is made.
if they provide your cost basis, go with it by I think the IRS would disagree based on similar situations like Enron, Lucent, and 100's of other publically traded securities where fraud was involved.
