What happens when a MySQL Cluster node is disconnected
In short, MySQL Cluster isn't a good fit for your use case.

MySQL Cluster's shared-nothing architecture provides excellent protection against component-level failure.  When nodes fail or become unresponsive, Cluster takes quick action to disable affected nodes.  It does not focus on conflict resolution, instead works to avoid the "split-brain" problem where a single cluster begins processing work in parallel without coordination.  This is exactly the opposite the use case you describe:  Database activity continuing as normal when partitioned by the network, to be reconciled later when everything reconnects.

MySQL Cluster also typically does not fare well when nodes lack low-latency connections.  Relying on WAN connections between nodes is a bad idea.  MySQL Cluster does support asynchronous replication between data centers.

You might consider using multi-source replication in MySQL Server 5.7 as an alternative.