Enterprise Vault 8 w/EMC Centera

Our environment is currently running EV 8 with an EMC Centera storage device.

Ideally I would like it to perform in the following manor.

-Email messages that are older than 90 days get archived off and replaced with a shortcut
-Archived messages never expire
-Archived messages are deleted when the user deletes the shortcut
-After the user deletes the shortcut a message can still be retrieved for up to 6 months

I have the following configuration
-Mailbox policy archives messages older than 90 days, creates a shortcut, and deletes original message
-Desktop policy set to "Both Deleted" for shortcut deletion
-Site properties set so users can delete items from their archives
-Site properties set so items are not permanently deleted for 180 days
-Retention category set to retain items forever
-Retention category is NOT set to prevent deletion of archived items
-Vault store partition retention period set to never

The problem that I have is that my Centera is currently configured for "Governance" mode and my users are not able to delete from their archives.  My understanding is that in order to fix this there are two potential options.  1) I can set the retention category to retain items for 0 days or 2) I can have the Centera reconfigured for "Basic" mode.  My fear is that if I go with option 1 that if expiry was ever accidentally run that it would delete all of the data. 

Does anyone have a similar environment and requirements that can share their experiences with me?

Anybody have any thoughts or suggestions on how I should proceed?

Can anyone verify with certainty that if I have the Centera reconfigured that it will allow deletion without altering the retention period?

Thanks
-Dave