It might just be cleaner to close the github repo and when other projects find a 404 where it used to be, they'll have to use super detective skills (i.e. Google it) to find the project's new home. And if they can't find it that way, then nothing of value was lost. (Yes, yes, I know it's more nuanced than that, but if you wanted permanence, you'd be hosting on your own domain, right?)

This would be a great way for them to accelerate migration away from Github.