As a minor point Homeguard, an ADF doesn't cost as much as many believe. Go to
here and enter KR87 in the search box. Especially if replacing a previous ADF installation. The KR87 is the most reliable ADF by far, with sealed electronics in the belly antenna.
I also think that while NDBs will be withdrawn for enroute nav (basically because almost nobody uses them
) they are not going away for approaches, and Europe is packed with NDB approaches. Short of putting in ILS everywhere (which won't happen), VORs (which won't happen), or GPS approaches (which may happen one day but you need a heavily EASA certified GPS to fly them), I don't see the need for an ADF going away.