hawk37:
Just an inquiry, I note you said "could", however, generally, would it be wings level, or would the loss of GPS cause the FMS to go into DR mode, and then continue to provide steering based on previous TAS and wind parameters?
When all the criteria were being develop all FMSes without IRUs would cause the wings to go level with loss of GPS. But, who knows what some bleeding edge avionics OEMs have done by now?
There are precious few birds qualified to fly RNP 0.30 (and conventional missed approach) that don't have at least one IRU. But, there are a few.