Briefly.
1. As of now, the claims about the demise of the navigator (by whatever name he may be known) are rather exaggerated.
2. There is a sizeable number of front line combat aircraft (eg the Tornado, SU 30) where the navigator has a place in the cockpit.
3. The point about aircraft-age is not true - yet. There will always be a role in MR aircraft.
4. Navigation and piloting are distinct and irreducible functions of flight; and often a division of labour becomes operationally necessary.
5. Operational necessity is the key; and the navigator (or indeed any other category) should bow out gracefully when the time comes.