This is a high-priority for us. By focusing on web-standards and avoiding proprietary plugins we're pretty confident that the content will be future-proof.

Something that could help is perhaps a choice that examples should work in (e.g.) Firefox recent.x on ubuntu, then provide a VM and archived version of firefox. Put it on a platform that archives things with C/LOCKSS and get a doi, then although you're not expecting people to use it on a daily basis, it'd cover several "worst case" kind of scenarios.

Of course that's not completely permanent, but would perhaps provide some more safety.

Also in addition to the sibling comment, the published articles will be on github under their organization.

I feel like binding the journal to GitHub means that it's less likely to exist over the long term (where long term means >100 years, which is as long as I would expect an academic article to be accessible for).

We produce "archive html" files where everything is bundled into a single file. We're looking into ensuring their long-term preservation with projects like LOCKSS.

Example: http://distill.pub/2016/augmented-rnns/index.archive.html

A simple intermediate step would be to archive with Zenodo