I've never used the Immortal Rules that Frank Mentzer created. Heck, it's only recently that I even had a look at them on .pdf, and I've never read them all the way through.
I doubt I ever will.
But recently, in his review of JB's BX Companion (sold out, by the way, congrats JB!), James Maliszewski mentioned in passing that he doesn't like the idea of quests for immortality in his games. I believe he said it doesn't fit the source literature he prefers.
I enjoy the same S&S stuff James does, but I also had a lot of my early gaming inspired by mythology of various sorts. And there, the idea of the quest for immortality stretches back as far as Gilgamesh.
Not to mention Hercules being granted immortality as the fruits of his labors, Qin Shi Huang Di (first emperor of historical China in the 3rd century BC) and plenty of Taoists searching for it, Egyptians mummifying their pharaohs, Norsemen trying to die heroic deaths so they could live on as einherjar at least until Ragnarok, and the twisted immortality sought by some vampires.
Not to say that Chevsky is wrong--it's purely subjective whether this sort of thing should belong in your game or not--but I think there's plenty of inspiration from real world sources that it should be an option.
Besides, what the heck else is there worth doing at levels above 30?