Homerj,
Read my post again. You asked about PRNAV departures, which DO NOT require specific navaids to be serviceable since they rely on the FMC accuracy to be sufficient to fly the correct track.
If the SID is an RNAV overlay (BRNAV unless is clearly specifies PRNAV), you cannot use that SID if the the U/S navaid is required to follow the SID track BELOW MSA.
If the SID is an RNAV overlay and the U/S navaid is used to define the track once ABOVE MSA, you can go because BRNAV accuracy (based on FMC position) is sufficient once you are clear of terrain.
I think you are confusing RNAV overlays and PRNAV departures.
P