According to the Nutanix Support & Insights, in a two-node ROBO cluster with a witness VM, if one node goes down, the other node sends a leadership request to the witness VM and goes into single-node mode. The cluster remains available and can tolerate another failure of either the witness VM or the network link.

Explanation
https://portal.nutanix.com/page/documents/solutions/details/?targetId=BP-2029_AHV:BP-2029_AHV Administrators can use Acropolis with IPAM to deliver a complete virtualization deployment, including network management, from the unified Prism interface. This capability radically simplifies the traditionally complex network management associated with provisioning VMs and assigning network addresses. To avoid address overlap, be sure to work with your network team to reserve a range of addresses for VMs before enabling the IPAM feature.
The Acropolis master assigns an IP address from the address pool when creating a managed VM NIC; the address releases back to the pool when the VM NIC or VM is deleted.

https://next.nutanix.com/installation-configuration-23/nutanix-vlan-34170