There is no automatic method of dealing with such a situation since such a situation is unlikely. Should the internet go down, we have much bigger problems to worry about than just Bitcoin fragmenting.

There is actually no way for a node to know whether the network has fragmented due to internet disruptions. How would a node distinguish between miners getting blocked, miners hardware failing and thus unable to mine, miners choosing to stop mining, or simply bad luck? There is no way for a node to know that there was a disruption.

Furthermore, a node doesn't know about the number of nodes online. The only way to know that would be to maintain connections to every single node, which a node is not able to do. It requires too many resources.

Bitcoin should not cater to this since such an event would be incredibly rare. Even if internet censors were blocking connections, methods of bypassing that through Tor and proxies will still bypass those filters and allow nodes to connect through firewalls, albeit slowly. Even so, miners could communicate with others around the firewall and a plan could be worked out to prevent the fragmentation of the network.