I agree A&C re GPS taking over, but the earlier suggestion was that a backup for some sort of total loss of GPS will be needed.
I thought the Americans were going for Loran for that purpose.
With no VORs, one would need an awful lot of NDBs to navigate around the place, at the low levels where GA is generally forced to fly in Europe! Can you imagine dead reckoning in IMC from one DME arc to the next?
I can't see VORs disappearing. But I can see non-approach NDBs (e.g. WCO) disappearing - what purpose do they serve?
TMM - I think the idea of dual NDBs on approaches is that when you are between them the two needles point towards each other when you are lined up with the runway - whereas with a single NDB you are working on the relative bearing which is harder.