Interesting discussion. I guess it is a very rare situation in aviation, and recommended procedures seem ambiguous. And importantly mayday relay may not be readily understood because it is so rarely used. In contrast, it is very common at sea and I am sure any professional seafarer would instinctively and instantly use mayday relay in equivalent circumstances. Also, there is no doubt that the pace of comms and indeed the rate of development of an emergency, is MUCH slower at sea than in your world.