When VCS tries to offline the Service Group it fails to offline Volume Resource with the error message

VCS ERROR V-16-2-13077 (Hostname) Agent is unable to offline resource(Volume_Resource). Administrative intervention may be required.

The DiskGroup never goes offline and manually needs to be deported.
This is because there are other Volumes in the same diskgroup not under VCS Control. These are vxsnap volumes created during backup.

Workaround:
Volume resources are optional so change the VCS configuration and remove the Volume Resources and update the Mount dependency as follows:

# hares -delete

and relink the Mount resource to Diskgroup:
 

# hares -link