If your RAIM limit is exceeded, you just notify as per AIP ENR 1.1 Section 21.3 and a different based separation standard (ie. non GNSS) will be applied.
Maybe the Ranga could confirm?
I'm not the Ranga, but the
non-surveillance separation standards available to ATC currently do not accommodate anything under 7NM CEP (= RNP2 for ATC). The non-surveillance Towers cannot practically use this standard either as they do not have the same tool that the Centre has for computing lateral separation on the fly.
There is one exception and that is where the aircraft is on final for an RNP approach (read old RNAV GNSS approach), when the final approach course can be considered equivalent to a LOC for separation purposes.
Incidentally, terrestrial navaids (even NDBs) can usually provide better separation solutions in terminal areas than RNAV standards.
Finally, plan
NAV/RNP2 and whatever else you're qualified and equipped for!
