Here is an SSRN abstract for a law review article on the validity of releases of ERISA benefit claims.
At one point, the author says: "In District 29, United Mine Workers of America v. New River Co., [842 F.2d 734, 736 (4th Cir 1988)] the Fourth Circuit held that an individual settling a wrongful termination grievance against a company (the “Initial Employer”) may have thereby unknowingly given up his entitlement to lifetime medical benefits. This holding illustrates why the Proposed Fiduciary Release Rules are required by ERISA to apply fiduciary principles rather than contract principles to assure that participants receive their earned employee benefits." The author's discussion of this case makes me think that perhaps current Fourth Circuit law is not in accord with the author's view of what ERISA requires. The author also cites Davis v. Bowman Apple Products, 2002 U.S. Dist. LEXIS 6204 (W.D. Va. Mar. 29, 2002), in which one of the judges of the W.D. Va. "relied on the totality-of-circumstances analysis . . . to invalidate a release of a participant’s breach of fiduciary claim for pension benefits."
Having scanned the article, I'm not sure that I understand or agree with all of it, but it is very interesting.