ADF to stay?
I think that ADF is likely to stay, Jamming of GPS is quite easy to do with a low powerd signal over a wide area.
Jamming ADF & VOR over a wide area would be almost imposable, as VOR's are very costly it would seem that ADF/DME would be the best back up in the event of an "attack" on the GPS system. This also has the advantage that the DME is used as the second choice for navigation by most airliner flight management systems.
And also how on earth am I going to get the cricket results half way down Africa with out the ADF?