of course it depends on the scale of such a war, would it be a single nuke dropped in a small country or will it be a global nuclear war between the big countries that already have a huge nuclear arsenal?! in my opinion a nuclear war is going to be global even if it starts with a small one, others would join in to wipe out the rogue country who launched the attack to protect themselves.
right, there are a huge number of scenarios that affect the overall outcome very differently.
If Europe was attacked on a large scale, the global internet becomes very damaged. A huge amount of global internet traffic is routed across the Atlantic and through the Middle East/Eurasia through Europe. Under-ocean links through Africa-South America, maybe from Iceland through Scandinavia (although that's kind of an easy target) might survive in optimistic scenarios about attacks that destroy Europe. If there are any pan-Pacific links, I doubt they're particularly high bandwidth or varied in route.
But if Paraguay suddenly revealed it's secret nukes and went rogue, I think the problem wouldn't be
so serious, although there'd be alot of people in Brazil/Argentina/Uruguay that'd be kind of pissed off with the outcome.
If the US, Russia or China went nuke-happy, well, good luck everybody. The threat of any one of them doing so serves as basically a veto on any decision made by anyone anywhere in the world, because there's just so little that anyone can actually do about it, there is no way of handling it other than finding somewhere good to wait it out. Internet? Forget it.
As long as someone has a copy of the Bitcoin source code, they can continue to run a node and continue to maintain the network.
The source code is overlooked in it's importance. I doubt it's as well distributed as the blokchain itself, and there isn't an efficient & automated distribution mechanism for the code either. Github really is a terrible model overall, hopefully Github will start interfering in repos and/or censorship soon (a likelihood now that Microsoft bought it), it'll push everyone towards a decentralized git solution.