If I may be brave enough to add to this discussion...
I think things will be far better than you imagine. First of all, I doubt everything will be switched off by 2015.
2nd, I imagine by 2015, the quality will have grown.
I would say, but for a few diehard audiophiles, the quality of DAB is better than with analogue, and the price of cheap DAB radios is not really an issue, even for the old folk.
I have always enjoyed FM, and have a nice Sony tuner, which way back when I thought was quite expensive, but it hasn't been listened to in 2 or 3 years, and I mostly tune in to radio through the TV, or more frequently through internet radio, and LastFM.
Yes, the current quality is not audiophile grade, but I can't see it being too long before they up it. Most people could stream full quality MP3 or similar, or even higher quality through their broadband connections. Personally I haven't heard a tuner that can compete with a full quality MP3, played through a decent system.
So ultimately I doubt most people will actually care. And analogue is certainly a massive waste of bandwidth in the todays world.
I liken it to digital cameras. Only 10 years ago I had friends hating them, but now, the quality has far improved, and a film SLR cannot compete in quality with even a fairly medium quality digital. I have a Canon 40D, and compared to the last film camera I had, it is like a whole new world of detail.
Some people mistakenly see analogue as giving you ALL the information, and rightly say digital always removes some of that information, but then you are at the mercy of recording media... An LP can only give you what a piece of fairly soft plastic open to the elements will give you... It isn't EVERYTHING. A CD at it's best is as good as or better as LP at its best IMO, and a well ripped bit perfect CD, played losslessly through a good system, goes even better. And now we are even getting some fantastic quality downloads from the likes of Linn (who were once making waves when they dared actually make a CD player! I remember the WHF review!)
The same thing will happen with DAB/FM, given that there is at least 5 years left for DAB to improve.
I for one won't be mourning it.