Hi,
You can use vicfg-backup command to take backup of certain about configuration of ESXI host using VIMA. Else you can use Host profile to capture main configuration of ESXI host then restore it to ESXI when the upgrade is un-successful ( When using vIMA or host profile , you have to re-install ESXI host to restore back the some setting captured using this tools. )
-- Note : Usually user just re-install ESXI host if it fails while upgrade and use host profile to restore the settings.
Regards
Mohammed