There is no federal statute of limitations for reimbursement claims. Thus, a court will borrow the analogous state statute of limitations to determine the limitations period. Your insurance company’s ERISA subrogation rights come from your insurance plan.
Therefore, a reimbursement provision under § 1132(a)(3) is most closely analogous to a simple contract action. Under South Carolina’s statute of limitations (S.C. Code § 15-3-530), insurance companies have three years to file a contract claim unless your plan says otherwise.