Earlier quoted context omitted.
I guess you can last 10 years, which is apparently what "This Page is Designed to Last" aspires to, but what if we have greater ambitions? Like 100 years?
Then I think you need something like archive.org. You can design and mark-up content that will still be useful and readable in 100 years. You might be able to preserve the presentation logic (CSS-style) for 100 years. You probably won't be able to preserve the interaction design for 100 years (without a dedicated effort -- that's why they bury computers along with the software in time capsules). But I think it is opt…
I can see a deletion heuristic that considers both account activity and repo activity being deployed within the next 10 years.
However I expect another evolution in SCM in the same timeframe.