Projects deleted from GitHub should be removed from Packagist

I ran into a project on Packagist ([kherge/doctrine](https://packagist.org/packages/kherge/doctrine)) that refers to a GitHub project that no longer exists. As far as I can tell this makes this package broken as nobody will be able to install it.

I asked #composer-dev how things like this should be handled. kherge looks to be active so it would probably be easy enough to send a ping and request the maintainer delete the project (if it is within the limits), but in the case that a maintainer is not able to be contacted what should be done?

Igor suggested packages be removed if their repository is throwing known "this thing has been deleted" responses for at least a certain period of time.

> maybe set a deletedAt flag the first time and if that exceeds 5 days, remove the package? — @igorw

Would 5 days be enough? Is there something already in place that we could bolt this onto? Maybe the "deleted branch" pass or something?

Of course the downside would be any project whose repository is legitimately down for an extended period of time and just happens to miss a couple of cycles of "are you still there?" requests.