If someone files bankruptcy, and then finds out a rich relative dies and is in line for an inheritance, how will that affect the bankruptcy proceedings.

Yes, if he collects the money prior to the bankruptcy being final, he would have to declare the income from this and most likely the money would have to be used first to pay off the people they owe before he would get any of the money.

But of course they owe the money, and now they have the money, so that is only right