Dont forget to clean up your
/etc/rc
file as it will have the VIF in there as well. If you dont it will be created at next reboot.
In your place I d go about this by:
1. Make sure its not in use by: resetting VIF stats (ifstat -za)
2. check ifstats > ifstats -a
3. if at this point your are confident the VIF is not in use;
a. vif destroy vif-name
b. ifconfig vifname down
How you go about this is up to you, but I suggest you clean up the RC file too.
Cheers,
Eric