In Sexton v. Continental Cas. Co., 1991 OK 84, 816 P.2d 1135, the Court held that the rule does not apply when a UM carrier denies its insured coverage prior to the settlement and release of the tortfeasor. In reaching its decision, the Court in Sexton recognized that whether destruction of the UM carrier's right to subrogation constitutes a complete defense to its insured's action on the policy "depends upon whether there is a prior breach of contract or waiver or estoppel on the part of the insurer which of itself cancels out its right to demand subrogation as a condition of payment." Id.