"[H]ow do we protect the fiduciary from a participant's breach of duty claim should an insurer become insolvent years hence, and be unable to the pay the retirement benefit otherwise promised under the annuity? ... [W]ouldn't the fiduciary be protected by ERISA's 6-year statue of limitations under ERISA section 413? ... [I]nsurance companies do not become insolvent overnight.... The public, at least those which follow the financial services world, have long notice of something currently being amiss in an insurer's balance sheet."