JFK - LAX. 2475 NM sector - then suddenly depressurized - with substantially higher fuel consumption.... Which would you choose? Point of Departure, or Destination.
Irrelevant, as ample alternate fields lie enroute, from chicago to Denver to Kansas City to Salt Lake City, etc. A hundred or more possibilities.
You suggested some mythical point of no return over the Rocky Mountains, as though they're some insurmountable barrier that can hardly be tamed. The truth is that from FL350, they're a little bump far below, and it's hardly an issue at all. As stated correctly before, if the departure is appropriate and nearby , then choose it. If one is close to the destination, then choose that. Otherwise, divert to any necessary, appropriate, available airfield. This is not rocket science. Closer to Kansas City? Go there. Closer to St. Louis? Go there. Closer to Chicago? Go there? Going south and Dallas is closer? Go there. No end of places to go. Boise? Sure. Albuquerque? Yep. Denver? You betcha.
Do any of these need to be previously "declared" alternates or part of the flight plan? Of course not. One diverts as required. Does one plan out each of these fields as a diversionary alternate? No, of course not.
Does one plan a series of diversionary alternates when crossing the rocky mountains? Of course not.
When overflying The Himalayas? Not necessary. Are we going to drop down, go around this mountain and then that, then connect with a lower airway and follow that? Doubtful. Point for the destination, notify ATC (such as it may be in that part of the world), and go in that direction, taking lower when able. Again, not rocket science.
and like fuel, it is NOT an infinate amount.
It doesn't need to be.
Guppy....I've gleamed very little from your various responses, except that you infer that you operate an "Oceanic..." capable aircraft "...within several feet of mountainous terrain..."
Actually no, I didn't say that. Your reading comprehension skills severely lack, but given your disjointed posting and your lack of understanding of your topic material, this doesn't come as much of a surprise.
One of my jobs (I do several) involves flying airplanes, some large some small, very close to terrain while engaging in wildland firefighting. Another job involves flying aircraft globally, including frequent oceanic crossings. These represent much greater distances with far fewer alternates, and are more critical and more significant than crossing a mountain range such as the alps, the himalayas, or the rockies...because one can't descend much due to fuel burn.
We never calculate equal time points with diversionary paths for routings over some of the areas discussed (Afghanistan, etc), because it's not necessary. There are options. Again, as you have trouble keeping track...one does NOT need to always consider the departure or destination, and there are generally plenty of alternate options enroute, even in remote parts of the world, should the need be. The only time this is not the case is during times of widespread weather (such as a cyclone), or on extended oceanic legs (when we do plan for alternate diversions...and in fact plan several types of alternate diversions, including depressurization).