I used to once believe, that a lot of what is on the internet lasts forever. It was a little naive to think, because over the course of my time online, I've seen things that I thought would last, ended up not lasting.
I would sometimes cross-search old usernames of mine because I do get around online. I can only now see my past accounts that I've made at least 5 years ago. Only 2 accounts that I recall, are 10+ years old when it used to be a bit more. It tells me that things will shut down eventually and it'll take down many accounts with it.
Unless you are on platforms hosted by Google or Microsoft by using their services, it's going to last for a long time because they're a little too big to just simply vanish overnight.
Your best option is to just back up what you can and if you remember to before you die, make arrangements for preservation purposes with instructions to those you'd want in on it.