You don't really need to do anything besides a normal `git clone`; any clone is as good as any other, really.
If the project disappears from Github someone would need to find a different place to host collaborative development, though. Maybe there needs to be some sort of Github-alternative in a friendly jurisdiction for projects that are too controversial to host on a mainstream provider in the US? E.g. for DMCA-violating projects, video codecs, DRM removal tools, etc.? I'm not that familiar with the alternatives but it wouldn't surprise me if there are better options in terms of resistance to US court orders.
If the project disappears from Github someone would need to find a different place to host collaborative development, though. Maybe there needs to be some sort of Github-alternative in a friendly jurisdiction for projects that are too controversial to host on a mainstream provider in the US? E.g. for DMCA-violating projects, video codecs, DRM removal tools, etc.? I'm not that familiar with the alternatives but it wouldn't surprise me if there are better options in terms of resistance to US court orders.