When you unextend a Network Extension, when you expand the network entry you have an option to select 'Connect cloud network to cloud edge gateway' after unextending to connect the remote side gateway.

By default, the cloud segment is left disconnected from the Edge Gateway after removing the network extension. This is done to prevent an Edge Gateway from advertising a route to the cloud segment and causing a potential routing conflict with the network in the on-premises data center. Selecting this option connects the segment to the Cloud Edge Gateway after removing the network extension. If dynamic routing is activated, the network is advertised from the Cloud Edge Gateway.

Unextending a network removes the HCX L2 bridged path without removing the NSX Segment or vSphere Port Group, or NSX interface. The NSX router interface remains disconnected when the option Connect cloud network is not used.