> The question is, is wordpress going to be around in 70 years? No one knows. But that static HTML page will still render fine
The question isn't whether wordpress will be around in 70 years, but whether it will outlast your self-hosted website. Anything that is self-hosted requires significantly more financial/logistical maintenance, and what is the likelihood of someone continuing to do that for 70 years?
For me it's very easy because those domains are also tied to my email and all of my other hosted services (gitea, tt-rss, etc.) all use the same domain. So it's very easy to remember to keep them all alive and active. I've had domain names active far longer than Wordpress has existed.
The question isn't whether wordpress will be around in 70 years, but whether it will outlast your self-hosted website. Anything that is self-hosted requires significantly more financial/logistical maintenance, and what is the likelihood of someone continuing to do that for 70 years?