I'm nonetheless struggling with the idea of a Mayday call for an uncomplicated comms failure. Hard to see the 'grave and imminent danger requiring immediate assistance'.
But doesn't the question of when to declare an emergency depend on that particular pilot's individual assessment of their ability to handle situation they are in? E.g. As a ppl with no IR if I had a choice between either continuing VFR flight into IMC or declaring an emergency to get me onto the ground at a controlled field it would a no brainer to declare a mayday. An IR rated pilot in that same situation would simply shrug their shoulders and continue IMC.
A very inexperienced PPL (as 150 Driver said he was at the time) suffering radio failure who has never flown non radio could easily panic. This panic itself could then become the "grave imminent danger"... Ref the sad fatal accident at Southend a few years back where a student pilot was turned away from a final approach due to ILS traffic. The unfamiliarity of the situation confused/panicked him and he ended up stalling into the ground because he forgot he was in landing configuration.
On the basis of accidents like the above I would always err on the side of advising pilots to declare whatever they feel is right at the time. Sweat the details once you're safely on the ground!