Check the statute. My interpretation (and that of a number of court decisions) of the provision to the effect that the AP may be treated as a surviving spouse to the extent provided in the QDRO is that in a DB plan with a QPSA, the AP must be expressly awarded some interest in the survivor annuity or the AP will get nothing if the AP does not start benefits (the 50% portion of the pension benefit described in the post) before the participant dies. One way to look at it is that the death benefit is a different benefit that the regular benefit. If the AP is not awarded some of the death benefit, the AP gets none.
While the proposition is untested, I think that the plan can adopt QDRO procedures that have a default to cover the failure to include a provision addressing death benefits (which is legal malpractice). For example, the QDRO Procedures can provide that, absent terms in the contrary in the QDRO, the result of failure to specify the AP's interest in the QPSA will be as suggested by Calavera: the AP will get the death benefit associated with the portion of the regular benefit awarded to the AP. I do not recommend such a provision on the QDRO procedures.
What can be argued on behalf of the AP is that the AP should be compensated for receiving nothing from the plan by the malpractice insurance carrier of the AP's lawyer who failed to assure that the AP did not get stiffed (pun intended) by the pre-retirement death of the participant, to the delight and benefit of the subsequent spouse.