$12/year domain registration and $3.50/month VM would probably host it just fine if somebody remembers to set up the recurring monthly/yearly billing correctly.
15 years ago, somebody might have bet on a Yahoo! product as something that would obviously be around for a long time.
It’s best not to make long-term plans on giant corporations’ products unless you’re paying them the kind of money that comes with an actual service agreement.
A small VM that you can easily move to a new host is a better bet than free hosting du jour at $web_giant.
15 years ago it might have been Lycos or Geocities, today it might be GitHub Pages or Netlify. I’m not sure about 15 years from now, but if web browsers as we know them are still around then, there will almost certainly be a service that can host a bit of HTML/CSS/JS around too.
A small VM needs to be periodically updated, both due to changing web standards (e.g. an old TLS version becoming deprecated) and to prevent it from becoming compromised; at some point, an OS upgrade will become necessary; the service provider might deprecate an old VM format and require a migration to something else entirely.
If the author already does all of that, sure, there won't be any or only very little incremental effort. But weren't we talking about the specific risk of the author losing interest (not financial, but in maintenance) in a small pet project?
Now just contrast all of that with uploading one or a handful of HTTP files to a new server and a bit of configuration at the hoster or your domain/DNS provider.
Static web hosters are also plenty and much more economical (in terms of money and server resources) than running your own web server, and for the reasons above, I wouldn't really consider them "less autonomous".
You still need to rely that the registrar and registry keeps operating for 10 years. For .com and common TLDs you can reasonably rely that it will keep operating forever barring some sort of general collapse of society/the internet. These newer TLDs? Maybe a bit less. Registrars like GoDaddy or Namecheap or whoever may go out of business, too.
I've got a (static) site that I want to live for a long time, the hosting provider does allow for deposits from others, so I'm hoping to make a large deposit with the hosting provider, but also include the necessary info to allow others to pay the bills if the deposit runs out eventually. Hopefully the company stays around.
Worst case, someone can bring it back from the internet archive and give it a new home, as I did.