Howdy! I'm an early digital photography adopter (1998), so I started feeling this pain a while back.
After the fourth photo service I had migrated to went out of business (and Picasa was then cancelled), I realized I needed something that wouldn't go away on me, and started working on PhotoStructure, a self-hosted photo and video "digital asset manager" that does automatic organization and deduplication to sweep everything into a single, neat, timestamped pile, and, critically, _keeps my original files intact_.
The point isn't to use PhotoStructure, specifically, but to use an application that you could walk away from and not be heartbroken, because that app used a standard filesystem hierarchy, and used standards to store any metadata changes.
My beta users asked me "how do I keep my stuff safe?" so many times, I ended up doing a bunch of research and wrote up this article, which discusses file integrity, why "3-2-1 backups" isn't really what you want, and how to go from there:
https://photostructure.com/faq/how-do-i-safely-store-files
Know that Google Photos is a great _secondary_ backup, but even in "original mode", what you upload aren't always the same bytes as what you download--their API strips off GPS metadata, I've seen changed captured-at times and exposure information changed after the round-trip through GP. (iPhone uploads, in "original" mode may survive the round-trip, but the point is that it's not something they guarantee).
I'd recommend using one of several mobile apps that will backup your original bytes directly to your computer at home. There are three I've tested and listed here: https://photostructure.com/faq/how-do-i-safely-store-files/#...
I'd also recommend using a filesystem on your home server that can detect media errors. I discussed that, and what cloud storage backups I recommend in the above article, as well.
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OK, so, now that you've got your stuff safe, let me tell you a story.
My Mom and Dad passed away almost a decade ago, and left several boxes filled with albums, shoeboxes and loose photos.
Almost none of the photos had dates on them. The albums had no writing in them, and most of the photos were of locations or people that I didn't recognize.
It took a while, browsing through these images, to realize that these images had relevance to only my parents: and maybe only the parent taking the photo.
Without additional context, these boxes of memories were almost entirely irrelevant to the next generation.
It was a punishing realization for me. I know these boxes were important and relevant to my parents, but all but a handful of photos had relevance to me.
Digital photography at least has a modicum of metadata automatically.
But you should still consider you "heirloom" of hundreds of thousands of photos and videos to be _irrelevant by default_ to the next generation.
So, how can you add relevance to your corpus of imagery?
I think that can be helped to some extent with
1. software (PhotoStructure shows random "samples" of years to deal with browsing through gigantic libraries, and displays "streams" of related photos using common metadata attributes to browse across hierarchical trees)
2. rating and pruning (so people can browse only the "best"), but
3. I think the real answer to avoiding irrelevance is for you to tell the story behind the image to give it context and relevance. It doesn't have to be a novel, but even a couple words can inoculate the album from irrelevance.
Good luck!