no magic script will help you because each shop is unique. I would start looking at "symaccess -sid 123 list logins".  Start identifying systems that are not logged-in, see what initiator groups they belong to, what masking views they belong and what storage groups are being used.  I like to places devices into a device group and run symstat on that group for 24 hours or so ..to make sure i see absolutely no I/O. At that point i begin to carefully delete masking view.  I feel your pain but there is no silver bullet, just untangle the mess slowly.
I have been tasked with going through our VMAX arrays (2 x 20Ks) to clean up old storage (storage groups, masking views, port groups, initiator groups, and devices).  Our decom process for hosts and storage is horrific.  We are currently in the process of migrations to VMAX3 and XtremeIO, but I need to clean up the mess on our 20Ks during the migrations.  Does anyone have a script that can be run to identify storage devices that have been stagnant for a long period of time?  There is so much storage that I believe can be reclaimed on these arrays, just need some help identifying it.  Any help with my cleanup efforts would be greatly appreciated.  Thanks in advance!  blooney
Finding and removing decommissioned storage on VMAX