Yes if they start to nuke the entire part of this world and affecting the internet connection, the blockchain system which require miner will not be able to confirm a block and make bitcoin transaction stuck,by the way if the internet connection is still fine even after the nuke exploding everywhere, I'll just sit here in my "neutral" country, grabbing popcorn, and watch the latest news about the war while still watching youtube for fun lol.
I myself don't think they are gonna send their nukes anywhere and only person who can think of it is the leader of North Korea. As it is being speculated North Korea currently has a stock pile of 60 warheads and it is also said said that North korea can use only miniature sized nukes but still it can have a good impact. But the point is many of the countries in the Asia surrounding neighboring North Korea has Anti ballistic missiles. Japan, South Korea, India, China and Russia all have the capability to take down the nukes in air if there is no failure in the systems. So the chance of NK nuking every nation here is slim.