If the NSX Manager becomes inoperable, you can restore it from backup. While the NSX Manager is inoperable, the data plane is not affected, but you cannot make configuration changes.

There are three types of backups:
Cluster backup
This backup includes the desired state of the virtual network.
Node backup
This is a backup of the NSX Manager node.
Inventory backup
This backup includes the set of ESX and KVM hosts and edges. This information is used during a restore operation to detect and fix discrepancies between the Management Plane's desired state and these hosts.
There are two backup methods:
Manual NSX Manager node backup and cluster backup
Manual node and cluster backups can be run anytime as needed.
Automated NSX Manager node backup, cluster backup and inventory backup
Automated backups run based on a schedule that you set. Automated backups are highly recommended. See Schedule Automated Backups.

To ensure you have a recent backup, you should configure automated backups. It is important to run cluster and inventory backups regularly.

You can restore an NSX-T Data Center configuration back to the state that is captured in any of the cluster backups. When restoring a backup, you must restore to a new NSX Manager appliance running the same NSX Manager version as the appliance that was backed up.