Stone Cold:
DH , you should defer to your organizations policies instead of relying on the opinions proffered here . . The replies don't seem to indicate a knowledge of the requirements / setup / or various missed approach criteria and techniques .
I would add that DH has obviously not been through an RNP AR training program.
Just as an overview for the lurkers: there are two levels of nav redundancy required for RNP AR.
"Entry level" also known as single string, does
not require at least one IRU but is limited to RNP 0.30 for minimums, and RNP of 1.0 or greater for the missed approach. If GPS is lost extraction can be by whatever means is available, including DR.
For any minimum of less than 0.30, or missed approach of less than RNP 1.0, then at least one IRU is required (dual string) to provide stand-alone IRU position for extraction. Missed approach protected airspace for a missed approach of less than RNP 1.0 requires the missed approach laterally protected airspace expand at a rate greater than the presumed decrease in accuracy of a stand alone IRU.