You can still do that, though. In Dhall you may import things remotely as you develop and then tell Dhall to pre-fetch the result, you can commit that and it will not access anything.

You may also just download any imports yourself and source them locally.

Additionally Dhall supports import fallbacks, for example you may try first a remote import, and if it fails it will look for another place, which I’ve could be remote or local. This is a good strategy for developing locally and then committing imports for production use.

You can also, of course, host the files in your local network.