Say a law firm closes its doors, whether due to bankruptcy or whatever, but still has a client's will or other legal documents. Does another law firm come in and assume responsibility to carry out the will of the client, or look after other documents? What happens?
In general, the firm will contact clients for whom it is holding documents to ascertain if they want the documents transferred to another firm or sent back. Also, in a medium to large firm, its probable many of the lawyers will be moving to other firms, and will take matters with them.
If a client cannot be reached, the firm is obligated to insure safe transfer and storage of those documents.