I agree with the above comments - this seems to be a circumstance for which the abandoned plan program was designed.
As for using the King case, I don't see its relevance. The issue there was whether income should have been recognized under the accrual basis of accounting in a year which was then closed under the statute of limitations. The critical difference was that the doctors in the King case filed tax returns triggering the commencement of the statute of limitations. Has the trust for the plan filed its tax returns? How about the revocable trust for years after the death of the husband? Another way of looking at it is to ask when a taxable transaction vis a vis the widow take place?
The more likely scenario would be that the trust continues to be treated as tax exempt and that none of the beneficiaries are taxable until there is a distribution. IRC section 402. Different treatment might result if it is determined that the trust was disqualified at some earlier point in time but its hard to say that that would help. Since the trust presumably was not filing any returns, the statute of limitations presumably did not start to run. Thus, it's hard to see how this would work to your advantage.
It is not unheard of to go amend a plan to bring it back into qualified status. Most practitioners would view this as providing the best result rather than filing tax returns for the trust for each open year.
In short, I think it is just wishful thinking to ignore the separate existence of the trust - especially since the investment firm has a reporting obligation and seems to be holding your feet to the fire on following the terms of the plan and trust.