Bear in mind, though, that the technology for dealing with these things are rapidly advancing.
I have an enormous amount of digital archives I've collected both from myself and from my now-deceased father. For years I just kept them stashed away. But about a year ago I downloaded the Whisper speech-to-text model from OpenAI and transcribed everything with audio into text form. I now have a Qwen3 LLM in the process of churning through all of those transcripts writing summaries of their contents and tagging them based on subject matter. I expect pretty soon I'll have something with good enough image recognition that I can turn loose on the piles of photographs to get those sorted out by subject matter too. Eventually I'll be able to tell my computer "give me a brief biography of Uncle Pete" and get something pretty good out of all that.
Yeah, boo AI, hallucinations, and so forth. This project has given me first-hand experience with what they're currently capable of and it's quite a lot. I'd be able to do a ton more if I wasn't restricting myself to what can run on my local GPU. Give it a few more years.
If there's someone who speaks the language then it isn't lost yet.
I suppose it's interesting to muse about what it means for the last person to speak a language before it becomes lost, but that's still just one person so it's kind an abstract, academic concern.