I.e., the tools will make up a plausible story, such as the story that best fits the available evidence excluding the forgotten bits? That's not very reassuring for those who worry about the loss of history.

I’m being slightly tongue-in-cheek, but what history can be researched or delivered in human-digestible form where the histories of the delisted at the scale you’re concerned about wouldn’t be so lossily compressed as to amount to roughly the same thing?

Not everyone will be delisted, the usual tools of extrapolation and demography are still available to the historian, and merely because information is not accessible via Google does not mean it is not available.