It will go offline at some point in the future, but since you don't know when, it's indefinite.
Could be when the money runs out (but costs may go up or down), or when the hosting company goes out of business, or stops providing this service. Or if they decide to do a KYC check and can't contact you.
If you keep it clean HTML/CSS, they could just click index files, I suppose.
This is my site mad on Linux/Markdown, with bash scripts.
Could this be a peer-to-peer problem? What if we have a distributed way of hosting and maintaining domains for legacy websites? It would be an interesting experiment.
Its very different to what others will suggest, but it will cost nothing and is easy to do.
Convert the HTML/CSS/JS bundle into a base64 url
If it fits in that scheme, the base64 url can basically act as a hash for the website.
As the long as that base64 url is saved somewhere, you can run the site by pasting it into the url bar.
Then its just a question of storage
- Internet archive
- Hard-drives
etc