Why would elves be ignorant of the process? They've been around forever. I know their memory can be dodgy but that seems fairly integral to your well being.
Also, why would the Stillmist be necessary? Assumedly, elves could do this before the Stillmist was created. So while powerful druids might be necessary for certain cases (and what counts as a powerful druid really, do they have Talents at 4 or something? Or are they just Healing 3 Druids?) I'm unclear on what's happening here.
in my game there are lots of reasons this would be true. Elves are diverse, only a few have studied arts beyond comprehension and are still around, many have moved on to ents, or are just rubies to be consulted. In my game no elf still alive knows of the separation of the white pearl from the bodies of the now halflings/goblin race, and only a few rubies might be around that have elves with that knowledge and fewer still that would talk of it. Also in my game only NPCs at this time can practice Rank 4 or higher magic. I've pegged the proper ability to Rank 5, which limits those that would be exposed to or have that knowledge. I've also set up a plan for sacrifice of something to gain something, xygofer and his daughter come to mind, so not many elves would wish to or be able to sacrifice something of themselves to meet the criteria for a nearly instant rebirth, and because there is a much easier and much safer method of rebirth that still happens in a time frame they are willing/happy to make most have rid themselves of the burdens of carrying any other memories of any other process, because why remember something difficult and unobtainable when the beautiful solution is right in front of you. Sure they may be able to make a difficult lore roll if give some book of knowledge or a prompt of some song that has an odd original phrase that was replaced by a more acceptable phrase, or some such but they wouldn't know much, and maybe only a name of who might know more.
At least in the game I ref hope to keep playing long enough for it to be something that happens. In my game 3 of the 5 rolled elves as a their kin, so it may be more likely than not.