That's fine for some circumstances in more conventional instrument flying, but entering the final segment in some RNP AR approaches (say RNP of .2 or less with an RNP required missed approach) is literally going into an area where extraction should be the rule when any significant part of the avionics fails.
A single GPS "unit" failure (in a dual GPS system supporting a dual FMS) should not affect the position solution just the redundancy. As long as ANP is less than RNP and there is no trending of the ANP increasing then risk has not increased appreciably. A single GPS "unit" failure was the only failure that we could continue with after the Final Fix. If it failed prior to the Final Fix the approach could not be continued.
It has been a few years since my airline and the regulator went down the RNP AR journey of discovery but I recall that the extraction was based on, dual GPS sensor loss, FMC failure and Engine failure at missed approach point i.e. Single FMC, IRS updating only.
This was for a RNP of 0.11 for Boeing and 0.10 for Airbus into an airport that the RNP AR approach was really the only option due to the terrain and has multiple RF legs to position into a valley.