Shared Nothing Live Migration protects you from planned downtime (say you need to patch Windows on host or replace or upgrade some hardware components). See:

Shared Nothing Live Migration

For an unplanned downtime you need either VM HA (little downtime, little data loss, VM reboots) or guest VM cluster (no downtime, no data loss, VM turns to other host). See:

VMs for High Availability

Guest VM Cluster for HA

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