Hi Shahul,
Per documentation, we recommend putting the system in Maintenance Mode, gracefully shutting down CWMS VMs and taking VM snapshots before starting the update. That way, if the update fails, you can just revert to snapshots.
I am not sure how vSphere takes backups of the VMs and what restore process for that is (maybe consulting VMware documentation would be of help).
If you have a backup on NFS storage, you can rebuild all the VMs and connect to NFS storage which will offer you to restore from backup. Information about this piece can be found in Disaster Recovery section of the Administration guide.
Kind regards,
-Dejan