You are wrong in that the stories do exist, however there are also reasons for them not to exist in some locations. To give one good example we have the story of Squanto that everyone knows - he was taken as a slave with a group of other Native Americans, and by the time he made it home he was the only one still alive out of those who left. Not only was he the only one still alive, but when he returned, his entire home community was dead, except for him. So there we have both a story of everyone dying but one, but we also have an example where there would not have been a story passed on were it not for Squanto having been far away AND for the fact that he affiliated with the settlers rather than being absorbed by a neighbouring nation that had not dissappeared. The nation that did not die out does not have a story of almost dying out, as it didn't, and since it absorbed the survivors of neighbouring nations, the survivors' stories can get lost easily. This isn't to say that those stories are always lost, just that they can be.

To give a better example I know more about - in the Nuxalk nation, first contact was in the late 1700s, with a European explorer accompanied by a collection of First Nations companions (Metis voyageurs). They didn't introduce disease at that time, but later on as diseases hit, people would deal with them through scattering, up until 1860 when smallpox hit so hard and so fast that out of a population of ten to fifteen thousand, there were less than two hundred survivors.

How do I figure the population? We have people in the area saying that they could hire several thousand packers within a days journey to help transport goods towards the interior. We also can see the remains of villages, with 20 to 25 large homes in them each normally supporting 40-100 individuals - and we know that there were some 50 villages, at least 15 of them existing as population centers at the same time (with others being more seasonal or temporary).

Now the important part relevant to your question - how did this die-off impact stories? As I start naming the villages going up the valley, I say roughly the following: village A, had these survivors from smallpox. village B had zero survivors, but one sister survived who was married to leader in village C, and his son carried both chieftainships (with the stories of both lineages now carried by one individual). Village D had no survivors, and no relatives survived, and their stories are lost.

Within twenty kilometres of where I am, at least four of the villages only had one survivor, and they passed as best they could their entire oral history down through just a few people. At least two villages died completely and also lost their oral history, meaning that there are large mountains in the valley whose names are not known because the families that were associated with that place disappeared.

So this is another aspect- connection to land. It's still common here to be told things like "when I was hunting up that valley as a kid, I came across a whole family who had lain down and died together, the mother and father holding the three children in their arms. The bones weren't even moved." These are stories that are connected to place, and because we still live in the same place, we still tell the same stories. When I see a creek, I tell the stories that happened there. When I see a mountain, I tell the stories of that mountain, but my part of North America is a little different from the areas that were impacted early on, in that almost all of those nations were relocated. New places, new land, and the triggers that helped pass on the old stories (which were already old at the time of relocation) were gone, and as a result the stories were told less.

This takes us to another aspect of this. My own ancestors went through a serious smallpox epidemic around 1780. around 70% passed away, and the survivors made a series of alliances with new nations, the Saulteaux and the Michifs, bringing them into the Iron Confederacy or Nehiyaw Pwat. I can tell you a bit of that history, mostly because I've learnt it, but the reasons this disease and die off isn't common knowledge in my own family's history is because much like the Cherokee and the trail of tears, we have our own tragic historical event, the first and second Red River Resistances, and the killing, relocation and generations of abuse and hand to mouth survival that followed lasting through into the fifties and sixties at least. When I dive into my family history trying to make sense of why my community is the way it is, I am told story after story of all the things that happened to us since those seminal events, as well as stories of how we have been rebounding since those events. We maintain stories from before these events as well, but in our collective consciousness these stories often serve more to establish what we aspire to than they do to give us a record of previous events. A massive die off that happened a hundred years previous, even if it was significant to our population, becomes far less important than you might think, given that the history after that event wasn't horrible, we rebounded and built new families with new trade relations.

So in summary, what I would say was this - stories were passed down, but in many cases survivors were absorbed into other tribes and took their stories. In other cases, the survivors weren't so concerned with passing down their stories of survival, but were far more concerned with passing down the ancient stories of their lineages, as it was those stories that gave legitimacy to land occupation etc., while the fact that we almost all just died was far less important.

In other cases, things like dislocation and intervening traumatic events served to emotionally and physically distance such stories, as they were replaced by far more long lasting stories of colonization.

This might seem controversial, but I think that most Native American tribes would choose decimation over colonization, or would rate colonization as the event with the larger negative impact on their communities.