How do you know the 401K company is out of business? They usually get bought or merge with other financial firms.

The company you worked for may have went out of business but the investment company that handles the 401K would have merged or would have been assigned to another firm.

If the 401K company changed, your work place would be aware of that. If your company you work for went out of busniess, merely look at your paper work as to who is the manager of the account