ACMS,
Contingency procedures are Airline dependent.(SOPS) and OP has a valid question,at least hes thinking about it.
No need to
.
The failure of an ND may make the PNF monitoring task more complicated but by no means brings the aircraft to become non RNP.
Getting the map on a lower DU would be acceptable but obviously not optimum as important items such VDS would not be in the line of sight of the PM as expected.
Some airlines require both NDs to work before the FAF and some leave it to the pilots.
FMCs scratchpad messages should be the ones taking all your attention.
I believe this is a quite good question and i will create a thread regarding RNP contigencies.