An attack on StackOverflow would be as bad or worse. These sites should probably be protected as areas of national strategic importance, like how the US protected the NYC docks during WWII.
It will be very interesting to see what entities are labeled as national security assets as the DoD begins to view 'cyber' a core battleground. What's the programming equivalent to a national strategic resource? How do you write the spec on that - "We must be able to immediately have access to 100,000 programmer-hours per 16 day period, at a skill level of no less than x% of industry average"? How do you implement that?
My thought is that, apart from core infrastructure, and expanding internal capabilities, there's not going to be governmental protection of businesses/American internet entities (aside from what protection already exists in the form of legal code), if only because it would compete/displace with already existing businesses (CloudFlare, Akami, etc) which is something the US is loathe to do (which is part of the reason why flood insurance is so messed up - there exists a program to help homeowners get flood insurance, but it's by law required to not displace existing insurers).
Not really. StackOverflow is mirrored and archived everywhere, like in the Google Cache. Github is read/write, and can't be mirrored anywhere near as easily.
The world would crumble/ it's probably some sort of weird national security scenario.