If a company had only one owner-operator, who administers its retirement plan after her death?

A recent BenefitsLink discussion points out a potential difficulty when a retirement plan’s named fiduciary is the plan sponsor’s sole proprietor and her death leaves doubt about who has power to administer the plan. (The inquirer described an investment custodian’s unwillingness to accept, absent a court order, instructions from a person many would treat as the sole proprietor’s successor.) https://benefitslink.com/boards/index.php?/topic/69560-orphan-plan-how-to-appoint-a-new-trustee/#comment-324850

Imagine another business similarly controlled and managed by its only owner. It is organized as a corporation or limited-liability company, but no one beyond the sole shareholder or sole member had been named as a director or officer, or as a manager.

Is a difficulty about who has authority to administer the retirement plan avoided if the employer/administrator is a corporation or a limited-liability company?

Does State law—whether about a corporation or company, or for decedents’ estates—provide enough authority for someone to manage the corporation or company, and its retirement plan?

What are your experiences about whether investment custodians and recordkeepers will accept instructions from someone who shows some reasonable explanation about the source of her authority?

What evidence or information is enough to persuade a custodian or recordkeeper to take instructions?

The problem is that there likely is no authority on point - especially at the state level.  We take a very practical approach - and would do so even in the case of the trustee issue you reference as being discussed in the other thread.  It is a "business" that sponsors the plan.  Regardless of the nature of the form of entity that business is conducted under, upon the death of the "owner/operator" the decedent's estate representative (Administrator/Executor) now has control as having indicia of ownership.  In a corporate setting, it's easy.  The estate rep now controls the shares, can call a special meeting of the shareholder, appoint themselves as director, etc., and then manage the business entity - including with winding up of the plan.  In pass through situations, it depends.  LLC's are more like traditional corporate structures and it's the same.  Sole proprietorships are the personal property of the sole proprietor/decedent, and as such, come under the control of the estate rep, who not only has the power to wind up the affairs of the business side of the decedent's "persona" but also probably has an obligation to do so as well (receivables?  Payable? - They are assets and liabilities of the estate).  The plan is both an asset and a liability.  The asset is the benefit due, the liability is the tax consequences if it isn't done right.  The estate rep steps into the shoes of the decedent to handle that as well.  In the other thread where the financial institution is being intransigent, I'd haul their a$$ into probate court - not attempt to get a court to appoint a successor trustee.  My experience is that probate courts don't mess with a lot of BS.  The asset of benefits due needs to be collected, the court can (and I've seen it happen) and will issue an order directing the holder of those assets to turn them over to the estate rep (as successor trustee or whatever) to get it wound up.  The financial institution now has a piece of paper to put in the file, and usually will comply.

MoJo, thank you for sharing your thoughtful view and helpful information.